H (letter). See Hotel (code). 1. A code or symboldesignating a kind of electronic navigational andblind-bombing system in which an airborne in-terrogator is used to measure distances fromtransmitting beacons at known locations on thesurface. Used esp. in certain specific designations,as Gee-H or Micro-H. 2. Used in combinationsto designate certain radar equipment used inWW II for navigation and blind-bombing, asin H2S or H2X. 3. Used as a symbol meaning'McDonnell Aircraft Corporation' in the desig-nations of Naval aircraft, as in F 2IL 4. A code orsymbol for 'altitude.'

If (abbr). 1. auth. 'Heavy' in combinations only.2. auth. 'Helicopter' in aircraft designations.See hel (auth abbr). 3. 'Hospital version,' in thedesignations of Naval aircraft so modified. 4. Notcapitalized. 'Henry/ a unit used in the measure-ment of electrical inductance. 5. 'Hydrogen/ asin /Z2O or H-bomb. 6. 'Honors/ as used in theVIP code fwhich see).

II (code suffix). 'Regular Air Force Female War-rant Officer' when used with a service number.

II-5A. A two-seat, Sikorsky helicopter adopted byboth the AF and Navy and used for air rescue.

The Navy designation is HO2S-1.H-5F. A four-seat, general-utility, Sikorsky heli-

copter used by both the AF and Navy.The Navy designation is HO3S-1.

H-17. A large helicopter powered by jet engines anddesigned to lift heavy loads, popularly called the'Flying Crane/

The H-17 was developed by the Kellett Aircraft Corpo-ration under subcontract to the Hughes Aircraft Co.

11-19. A twelve-place helicopter developed bySikorsky and used for air rescue and generalutility.

The H-iQ carries ten passengers or eight litter patientsin addition to a crew of two.

11-21. An all-metal helicopter with tandem rotors,developed by Piasecki, used esp. for air rescue.

1I-23A. An ambulance helicopter developed byHiller (UH-12B), providing space for two littersand one pilot.

This helicopter is built so as to be transportable in theC-i 19, and is provided with amphibious landing gear.See I-I-23B and HTE-2.

II-23B. The US Army version of the H-23A, modi-fied with a skid landing gear.

FlA (abbr). 1. auth. 'High altitude.' 2. Hour angle/3. auth. 'Home address.'

HAA (abbr). 'Heavy antiaircraft artillery.'HAB (abbr). 'High-altitude bombing.'hachure, n. Any of a number of short lines used

esp. on a map or chart for shading and indicatingrelief on the ground. Hence, hachuring, n., theaction of drawing hachures, or the hachuresdrawn.

hack, v. tr. To tolerate or put up with something.Slang.

hack watch. A special kind of wrist watch, usedesp. by navigators, so constructed that the worksstop when the winding knob is disengaged, allow-ing accurate setting. Popular.

The hack watch can be 'hacked,' or stopped, and setto within a second, i.e., the second hand can be synchro-nized with the minute hand.

Hadrian, n. A popular name for the CG-4.IIAFMed (auth abbr). 'Headquarters Allied Forces,

Mediterranean.'l i ahn Air Base. An air base at Iiahn, Germany,

named for the city.hail, n. Pellets or lumps of frozen rain or snow

sometimes precipitated during a thunderstorm.hair hygrograph. An instrument for measuring

and recording humidity, using specially-treatedhair, esp. human hair, as the sensing and activat-ing element.

The length of the hair varies with humidity.hair hygrometer. A hygrometer that measures

humidity by means of the variations in a spe-cially-treated strand of hair. See prec.

IIalberstadt, n. A two-place, German biplane ofWW I, used as a fighter and observation plane.

halflife, n. The length of time required for a radio-active isotope to decay to half its initial radioac-tive value, i.e., to lose half of the radioac-tive particles present through disintegration, icsatoms being converted into stable atoms.

The halflife of different radioisotopes varies. For ex-ample, C11 has a halflife of 21 minutes, C14 has a halflifeof 5,400 years. A substance that has had three halflifeperiods has one-eighth of its radioactivity remaining.

half-loop, n. A flight maneuver in which an air-plane makes one half of a complete loop.

The term 'half-loop' is usually applied to one half ofan inside loop, begun when the plane is in a normal up-right flying position. Siich a half-loop results in invertedflight at the finish. Cf. I nun elm a mi turn.

H

half-roll, 11. A flight performance or maneuver inwhich the airplane makes one half of a completeroll, i.e., rotates 1800 about its longitudinal axis.

A half-roll is begun from any position, but esp. from anupright or inverted position.

half-track, n. Also halftrack, (htrac) Specif. Amilitary automotive vehicle, usually lightlyarmored, having endless treads on sprockets andbogies in place of the rear wheels.

half-wave rectifier. A circuit, vacuum tube, orother electrical device that uses one alternationof an alternating current to produce a pulsatingdirect current. Cf. full-wave rectifier.

Halifax, n. A four-engine British heavy bomber ofWW IIj-developed by Handley Page.

HAM (aulh abbr). 'Heavy automotive mainte-nance.'

Hamilcar, n. A heavy-transport, British glider ofWW II, built by General Aircraft, Ltd.

A powered version of the Hamilcar mounted two en-gines.

Hamilton Air Force Base. An AF base at SanRafael, California, named for Lieutenant LloydA. Hamilton, recipient of the DistinguishedService Cross, killed in fighter combat in Francein 1918.

hammerhead stall. A term applied to an airplanemaneuver or performance involving a steep climbor zoom almost to the stalling point, then caus-ing the nose to drop sharply with wing over sothat the airplane reverses its initial direction offlight. Cf. renversement, n., wingover, ft.

ham operator. A licensed amateur radio enthusi-ast who operates a station as a hobby. Usuallycalled a 'ham.' Slang.

Hamp, n. An Allied code name for the JapaneseMitsubishi Navy Zero Mark II, a clipped-wingfighter of WW II.

Formerly called 'Hap' and later 'Zeke 32.'Hampdcn, n. A twin-engine British torpedo

bomber of WW II, developed by Handley Page.ham station. The radio station of a ham operator.hand, n. To fly hands of: See fly, v., note.handbook, n. In a general sense, any small book

containing specialized information or instruc-tions.

hand brake. A hand-operated lever for applyingthe wheel brakes on an aircraft.

hand-carry, v. Ir. To deliver or carry a letter,document, package, or the like to the addresseepersonally or by a special messenger, rather thansending it by a regular delivery service.

hand flag. A signal flag held in the hand.hand grenade. 1. A grenade designed to be

thrown by hand. 2. Specif. A fragmentationgrenade for throwing by hand.

handie-talkie, n. A miniature two-way radio for

short-distance communication, as within an in-fantry company.

The handie-talkie, such as the SCR-536, is small enoughto be held in the hand. Cf. walkie-talkie, n.

Handley Page. (ILP.) [Handley Page, Ltd., aBritish aircraft manufacturing firm.] Used in thenames of airplanes, as in Handley Page Halifax,Handley Page Hampden, or Handley PageHastings.

Handley l'uge 0/400. A large, twin-engine Britishbomber of WW I, developed by Handley Page.

hand ling line. A line or cable used to aid in mov-ing an aircraft about.

A handling line is sometimes used with a seaplane fortowing it out of the water; with a dirigible for towing andhandling it from the ground.

hand pump. Any manually-operated fuel pump,esp. a wobble pump, used either for priming anaircraft engine or as an emergency fuel pump.

ll&R (abbr). 'Holding and reconsignment.'hand ratehet . Any hand-operated tool, as a drill

or wrench, using a ratchet, which permits itsoperation either in complete rotations of the tool,or in oscillating or back-and-forth movements.

hand reeeipt. In supply usage, a form signed by aperson acknowledging the receipt of one or moreitems of supply.

hand .reel unit . In communications usage, a reelof wire mounted on a steel bar, carried by twomen when laying communication wire in thefield.

H&S (abbr). 'Headquarters and service/hand salute. A salute (which see, sense 2) accom-

plished in a certain prescribed manner by raisingthe hand, normally the right hand, to touch thehat or forehead. Usually shortened to 'salute.y

The hand salute is given by an airman to an officerand by a lower-ranking officer to a higher-ranking officer.In each case, the salute is returned. Salutes are also givenby all ranks to the tlag, the national anthem, a high official,and the like.

handset, n. Specif. The ordinary type of telephoneset, in which the transmitter and receiver are con-nected by a piece used as the handle, the wholeforming a single unit.

hand weapon. A weapon, such as a pistol, knife, orsword, used by one hand.

Distinguished esp. from a shoulder weapon, in regard tofirearms.

hang, v. To hang on the propeller, to reach a near-stall position in a steep nose-up attitude in anairplane.

hangar, n. 1. A building, tent, cave, compartment,or other shelter or place where aircraft arehoused, worked on, or tested, and often contain-ing associated offices, shops, etc., esp. a typicallyconstructed building with space inside open tothe roof, equipped with overhead tracks, hoists,and pulleys. 2. Such a typical building used as a

laboratory, such as the one at Eglin Air ForceBase. See climatic hangar.

'Hangar' is a French word, the ultimate origin of whichis uncertain. The O.E.D. shows its use as early as 1852,but in reference to a place in France that provided shelterfor a carriage. Used in reference to a shed for an aircraft,it appears to have been borrowed into English directfrom the French about 1902. Wilbur Wright used it in aletter of 18 Oct 1903.

hangar chief. A noncommissioned officer whosupervises the activities in a particular hangar,i.e., scheduling and supervising inspection andmaintenance of aircraft, and looking after theequipment belonging to the hangar.

hangar deck. A deck in an aircraft carrier, de-signed as a hangar.

hangar flying. The art or practice of conversingabout, criticizing, or rehashing flying experiences.Slang.

hangar line. The line formed by a row of hangarsalong with the areas immediately surrounding.See flight line.

hangar pilot. An untruthfully boastful pilot.Slang.

hangar queen. A damaged or disabled airplanekept for cannibalization. Slang.

hanger, it. Specif. Incorrect for 'hangar.'haiigfire, n. A brief delay of a round of ammuni-

tion in firing after being struck or subjected toother igniting action. Cf. misfire, n., sense 1.

hanging start. An act or instance of an aircraftengine or starter sticking or hanging during anattempted start.

happy valley. [Prob. from 'flak happy.'] A regionof intense flak concentration; specif., duringWW II, the Ruhr valley in Germany. Slang.

HAR (abbr). 'Honorary Air Reserve.'har (auth abbr). 'Harbor.'harass, v. Ir. To annoy and discomfit the enemy

with repeated small-scale attacks; to raid sporad-ically enemy supply lines, sea lanes, installations,or the like.

harassing gas. In chemical warfare, any gas thatforces the enemy to mask and thus harass andretard him in his military operations.

harcft (auth abbr). 'Harbor craft.'hard, n. A part of a beach with a specially-pre-

pared hardened surface extending into the water,used for loading and unloading directly into orout of landing vessels.

hard hat. A crash helmet. Colloq.hardstand, n. Any paved, compacted, or other-

wise specially-prepared surface or area set upeither for parking an airplane or ground vehicle,or for storing supplies and equipment; specif.,such a place set up for an airplane, normallyadjacent to a runway or taxiway.

A hardstand in the specific sense usually accommodatesonly one airplane, but it may accommodate more.

hardstanding, n. The facility provided by hard-stands, as in 'the base has hardstanding.'

hard start. An act or instance of starting an air-plane's jet engine using an electrical voltage froman external source.

hardware, n. 1. A category sometimes used todesignate certain equipment or supplies madeentirely or largely of metal and manufacturedfor hard use in the field. 2. A point-of-view termfor the physical aspect of a thing used, as dis-tinguished from its capability or function.

In sense 1, this term, as used by certain writers, coversnot only items bought in a hardware store, such as bolts,nuts, hinges, tools, fittings, and machinery, but also air-craft, trucks, tanks, and engines. The category excludessuch items as paper clips, pins, or other office supplyitems made of metal.

hard X ray. An X ray of high penetrating power.Hare, n. A code name for a general-purpose, single-

rotor helicopter designed by Mikhail L. Mil andexhibited in 1951 at the Tushino military airportnear Moscow.

Ilarlingen Air Force Base. An AF base at Har-lingen, Texas, named for the city.

harmonic, n. A harmonic frequency.harmonic frequency. Physics. A frequency which

is an integral multiple of a fundamental fre-quency. See fundamental frequency.

harmonic motion. In helicopter theory and anal-ysis, the periodic motion of rotor blades, occur-ring at either a single frequency or severalharmonic frequencies.

harmonize, v. Ir. To align the sights of a gun sothat the curving path of the projectile will meetthe straight line of sight at the target; to adjustor align the gunsight, guns, rocket launchers, orgun camera of a fighter so that an accurate aim isobtained at a given range, or so that the gunswill produce a desired pattern of fire. Hence,harmonization, n.

Cf. boresight, V.y and see pattern harmonization,point harmonization.

Harmon Trophy. Any one of several personaltrophies given annually for achievement in flyingmade from a grant established by Colonel Clif-ford B. Harmon (1866-1945), pioneer Americanballoonist and aviator.

Separate trophies are awarded to a man and woman,and separate trophies are awarded for international andnational achievement, the several national trophies beinggiven to nationals of different countries. The trophieswere first given in 1926, but awards were suspended duringWW II, except that after the war, retroactive awards weremade. Since 1945, two separate international awardsare given, that designated by the Ligue Internationaledes Aviateurs, which is presented by the President oithe US, and that designated by the Harmon trustees.One of the awards commemorates the Lafayette Escadrille;another award is given to a pilot of a spherical balloon.

harness, n. Short for such locutions as 'ignitionharness/ 'parachute harness/ or 'safety harness.'

flarvard, n. A name given by the British to theAT-6.

Referred to In its various modifications as 'Harvard I/'Harvard II,' etc.

HASC (abbr). 'Headquarters Air Service Com-mand/ Hist.

hash, n. A type of clutter appearing in the form ofunsynchronized signals on a radar screen. Popular.

hash mark. A federal service stripe. Slang.hassle, n. An argument, brawl, or fracas. Slang.Hastings, n. A post-WW II, four-engine, British

military transport and cargo airplane, developedby Handley Page.

hatch, n. A ship term sometimes applied to anopening or door in an aircraft, esp. one in thedeck of an aircraft or in the top or bottom of thefuselage.

In combination, as in camera hatch, cargo hatch, escapehatch, forward hatch, etc.

hat-in-ihe-ring squadron. A popular name forthe famous 94th Pursuit Squadron of WW I, so-called because of its distinctive insignia

The hat-in-the-ring squadron was the first Americanpursuit squadron to reach the front. Rickenbacker, Luf-bery, and other famous aces of WW I were members of thissquadron.

Havoc, n. A popular name for the A-20.Hawk, n. A generic name for certain fighter air-

planes, now all obsolete for the US services, pro-duced by the Curtiss-Wright Corporation; alsoused specifically for one or other of these air-planes, esp. for the US Navy's BF2C-1, a fighterbiplane, or the Air Corp's P-6.

Certain other planes in the 'Hawk' series were usuallyknown by such popular names as 'Seahawk,' 'Tomahawk,''Kittyhawk,' and 'Mohawk.'

Hawker, n. [Hawker Aircraft, Ltd., a British air-craft manufacturing firm.] Used in the names ofcertain British airplanes, as in Hawker Fury,Hawker Hurricane, Hawker Tempest, etc.

Hawks Memorial Award. An award establishedin 1939 in honor of Frank M. Hawks (1897-1938),noted American aviator, and presented annuallyfor outstanding contributions to the developmentof aviation. In full 'Frank M. Hawks MemorialAward/

This award is presented annually by the Air ServicePost 501, American Legion, New York, of which Hawkswas a Past Post Vice Commander.

hazardous duty pay. A species of incentive paygiven for any duty considered hazardous, as dutyinvolving parachute jumping or demolition ofexplosives.

hazard pay. Hazardous duty pay.haze, n. 1. A concentration of water vapor, lighter

than fog or clouds, but thick enough to reducevisibility. 2. A smoke concentration laid downaround or over a friendly force or area suffi-

ciently heavy as to hinder enemy observationfrom the ground but not so heavy as to impedefriendly operations.

HB (abbr). 'Heavy bombardment/H-bomb, n. The hydrogen bomb.HC (abbr). 'High capacity bomb.*Hc (code). In air navigation, a code or symbol for

'computed altitude.'hcptr (abbr). 'Helicopter/ILC.U. (abbr). 'Heavy conversion unit.* British.HD (abbr). 1. auth. 'Honorable discharge.* 2. auth.

'Harbor defense.* 3. 'Historical Division' in refer-ence to a division of the Research Studies In-stitute responsible for the USAF historical pro-gram, Air Force wide.

HD (code). 'Density altitude.' Also Hd (code).HDC (abbr). 'Harbor defense command.*hdlg (auth abbr). 'Handling.'hdsp (auth abbr). 'Hardship.*HE (auth abbr). 'High explosive.*

Used attrib., as in HE bomb, HE shell, HE filler, etcHe (abbr). 1. 'Heinkel.' 2. 'Helium.'he, pron. The pronoun usually applied to the

enemy, as in 'the enemy struck but his fire wasineffective.'

head, n. 1. The leading end of a formation orcolumn. 2. That part of a bomb or other missilethat carries the explosive or other payload. Seerocket head, warhead, n. 3. A latrine on anaval vessel.

heading, n. 1. In air navigation, the horizontaldirection in which an aircraft is pointed, i.e., thedirection of its longitudinal axis, usually ex-pressed as an angle measured clockwise fromsome reference line, such as true north, to thelongitudinal axis; specif., true heading. 2. In abroader sense, direction.

In sense 1, an aircraft's heading usually does not coin-cide with its track because of drift or yaw. Pleading,'in this sense, is often qualified with a word designatingthe reference line from which it is measured, as in 'compassheading,' 'magnetic heading,' or 'true heading.' See sepa-rate entries. The unqualified word 'heading' is somewhatambiguous, but usually means true heading.

head-on, a. Frontal. Also used adverbially, as in'they met head-on.'

head-on wind. A head wind blowing directlyagainst the front or head of a given aircraft, op-posed to its direction of flight.

headphone, n. An apparatus consisting of one ortwo earphones attached to a band or harness forholding them over the ears. Cf. headset, n.

headquarters, n. (hq) Construed either as a sing,or pi. 1. The command echelon of a unit or otherorganization, consisting of a commander and hisstaff. 2. When used in such designations as 'Head-quarters Air University,' or 'Headquarters TenthAir Force,' a unit made up of the commander and

his staff, together with the administrative andservice personnel, both officer and enlisted, whoprovide essential services for the commander andhis staff in the operation of the command. Thecommander of this unit is also the commander ofthe overall command, as the commander of Head-quarters Air Defense Command is also the com-mander of the Air Defense Command. 3. Thegeographical center of authority of any organiza-tion, i.e., the building, base, or other place wherethe commander and his staff are located.

As used in sense 2, the word is joined with the desig-nating second element without a comma intervening. Inthis sense, the headquarters is a manning unit. See unit,n., sense 2.

As used in the phrase 'Headquarters and HeadquartersSquadron' (now historical), the first 'Headquarters'referred to the commander and his staff, the second 'Head-quarters' designated the unit to which headquartersand certain other personnel were assigned for adminis-trative purposes. See headquarters squadron section.

headquarters commandant. In the head-quarters of certain air commands, a staff officerwith such assigned duties as the internal adminis-tration of the headquarters, the maintenanceand security of the buildings and grounds of theheadquarters, or other special headquartersduties as required.

Headquarters Command, USAF. A major aircommand in the USAF, established primarily toserve the area of Washington, D.C1 and provideservices for Headquarters USAF.

The functions of Headquarters Command, USAF,are to provide aircraft for, and supervise the proficiencyand administrative flying of, AF personnel in the Wash-ington area, to provide administrative and logistic supportfor Headquarters USAF and certain other organizationswithin the Washington area, to participate in domesticemergencies, and to perform certain other duties desig-nated by the Chief of Staff, USAF.

headquarters squadron. A term of conveniencealways used in conjunction with the word 'sec-tion/ identifying the headquarters unit as de-fined under headquarters, n.y sense 2.

headquarters squadron section. In certainlarge commands, an administrative staff section,with the characteristics of a unit, made up of cer-tain headquarters personnel and certain otherpersonnel with duty assignments in activitiesoutside the environs of headquarters, and func-tioning as an administrative unit in maintainingpersonnel records, preparing morning reports,conducting courts-martial, etc. The officer incharge of this section is a personal staff officer ofthe commander.

This section is called a 'section' because it is considereda part of the headquarters unit (see headquarters, n.,sense 2), identified for convenience as a 'headquarterssquadron.' Its purpose is to relieve the commander ofcertain court-martial and other administrative duties.

Headquarters United States Air Force. 1. Thecommand echelon of the USAF, which, under the

direction of the Secretary of the Air Force, formu-lates policies for the AF, plans and initiates AFactions, and supervises the implementation ofsuch policies and actions throughout the opera-tional commands. Usually called 'HeadquartersUSAF/ 2. The military unit made up of the per-sonnel of this command echelon.

Hq USAF is a component of the Department of theAir Force at the seat of the government, and is headedby the Chief of Staff. It consists of those offices and boardstogether with their personnel, both military and civilian,which constitute the staff organization that advises theChief of Staff and assists him in monitoring or supervisingthe AF. When this staff organization, or a part thereof,serves in the capacity of adviser to the Secretary of theAF, or to other authorized officials, it is sometimes calledthe 'Air Staff'; when serving with the Chief of Staff as headof the AF, it is called 'Headquarters USAF.' See air staff,sense ia, Chief of Staff, United States Air Force.

head resistance. The resistance of the air againstthe front of an object, such as an airplane,moving forward through the air.

headset, n. An apparatus or helmet holding a pairof earphones fitting over the ears.

headspace, n. Firearms. The distance between theface of the locked bolt or breechblock of a gunand some specified point in the chamber.

With guns designed for rimless, bottlenecked car-tridges, headspace is the space between the bolt face anda specified point on the shoulder of the chamber; withguns using rimmed cartridges, the space between the boltface and the ridge or abutment in the chamber againstwhich the rim rests; and with guns using rimless straight-case cartridges, the space between the bolt face and theridge or point in the chamber where the mouth of thecartridge case rests.

headward acceleration. Acceleration of the bodyin the direction of the head.

It is suggested that this term be used in place of 'positiveacceleration.' Headward acceleration tends to cause theblood to rush from the head.

headwind, n. Also head wind. A wind blowingfrom such direction that its principal effect is toretard the groundspeed of a given aircraft. Seehead-on wind.

Roughly, any wind coming in toward the nose from adirection within 45 either side of the longitudinal axismay be considered a headwind. Cf. tailwind, n.

HEAP (abbr). 'High explosive armor-piercing/heartland, n. 1. The area of a country vital to its

war-making ability; the interior of a country, asdistinguished from its periphery. 2. Geopolitics.A theoretical area on the Eurasian continent,conceived by the geographer, H. J. Mackinder(1861-1947), and others to be an area which, ifcontrolled by a single power, would give thatpower strategic advantage for dominating theworld. Sometimes called the Tivot area.'

In sense 2 the area cannot be explicitly defined, forwith different writers, and even with the same writer,it means different areas. The area has sometimes beenlimited roughly to Russia west of the Lena, sometimesextended to include Scandinavia, sometimes extended toinclude Turkey.

HEAT (abbr). 'High-explosive antitank.*

heated clothing. Clothing made with incorpo-rated electrical elements or plates used to giveheat to the wearer.

heat engine. Any engine or motor that convertsheat energy into mechanical energy or motion,as an internal-combustion piston engine, jet en-gine, steam engine, or rocket engine.

heat exchanger. 1. In a turbojet engine, a deviceor system whereby heat is transferred from theturbine exhaust to another part of the engineand used to heat the air entering the combustionchamber. 2. In a more general sense, any devicesuch as a water radiator, oil cooler, or the likeused to cool a liquid or gas by transferring heatto another liquid or gas.

heat seeker. A guided missile or the like incor-porating a heat-sensitive device for homing onheat-radiating machines or installations, such asan aircraft engine or blast furnace. Colloq.

heavier-than-air aircraft. Any aircraft weighingmore than the air it displaces; an aerodyne.

hcavier-than-air flight. Flight in, or with, aheavier-than-air aircraft.

Ileaviside layer. The E layer.heavy, n. pi. Heavy bombers, as in 'we saw a for-

mation of heavies.''Heavies' was used esp. in WW II to designate B-17

or B-24 bombers. The term is relative.heavy, a. (hv) 1. Of aircraft: a. Having great

weight, as in 'a heavy bomber.' b. Capable ofcarrying a load weighing much, as in a 'heavytransport.' 2. Of a gun: a. Having a large caliber.b. Having great weight.

In sense I, see medium bomber, note, transportaircraft, note.

heavy antiaircraft artillery. Artillery designedprimarily to counter medium altitude attack.

heavy artillery. Specif. Artillery, other than anti-aircraft artillery, consisting of all howitzers andlonger-barreled cannon of a caliber larger thanthose included in the classification of mediumartillery, Cf. heavy weapon, medium artillery.

heavy bombardment. 1. Short for 'heavy bom-bardment aviation.' 2. A bombardment of greatintensity, esp. one with large aerial bombs orother missiles.

heavy bombardment aircraft. A heavy bomber.Construed either as a singular or plural.

heavy bombardment aviation. That branch ofbombardment aviation that uses heavy bombers.

heavy bomber. Any large bomber considered to berelatively heavy, such as, in 1955, a bomberhaving a gross weight, including bomb load, of250,000 pounds or more, as in the case of theB-36 and the B-52.

During WW II, bombers such as the B-17 and B-24were considered heavy bombers. The B-20 was also classed

as a heavy bomber, although at first considered a veryheavy bomber. See note under medium bomber.

In combinations, as in heavy bomber force, heavy bomberoffensive, heavy bomber squadron, etc.

heavy caliber. Large caliber.heavy cargo aircraft. A heavy transport aircraft.

Construed either as a singular or plural.heavy drop. An airdrop in which heavy articles,

like trucks or artillery pieces, are dropped byparachute.

heavy duty. Constant duty, or duty under de-manding or adverse conditions. Said esp. ofequipment.

Ln combinations, as in heavy-duty aircraft, heavy-dutybattery, heavy-duty operation, etc.

heavy hydrogen. Deuterium or tritium.heavy machine gun. 1. Any aircraft machine gun

above 0.30 caliber. 2. In Army usage, any ma-chine gun of relatively heavy weight, including0.30 caliber water-cooled machine guns and 0.50caliber machine guns. 3. In specific nonofficialcontext, any machine gun designed to be mountedon a tripod, on an aircraft, or otherwise, andweighing approximately twenty-five pounds ormore without the mount.

As an antiaircraft weapon, a heavy machine gun(sense 2) is in the category of light weapons. See lightweapon.

heavy transport aircraft. A transport aircraftconsidered capable of carrying a relatively heavypayload; specif., as defined in special context, onecapable of lifting a payload of approximatelytwenty-five tons.

An example of a current type of heavy transport air-craft is the C-124. See transport aircraft, note.

heavy water. Any kind of water heavier in weightthan ordinary water; specif., deuterium oxide(D2O).

Heavy water, in its specific sense, has a specific gravity1/10 greater than that of ordinary water; it freezes atabout 40 C.

heavy weapon. Specif. Any antiaircraft weaponhaving a caliber of 120 mm or greater. Cf. heavyartillery.

In the Army, 'heavy weapons' is an infantry termapplied to mortars, howitzers, long-barrelled cannon,heavy machine guns, recoilless riiles, and other crew-servedordnance.

IIecht (code). A German air-to-surface guided mis-sile of WW II.

heckle, v. tr. To harass enemy troops, installations,etc. Hence, heckling mission.

HECP (abbr). 'Harbor entrance control post/HedCorn (abbr). 'Headquarters Command.'hedgehog, n. 1. a. A portable obstacle, made of

crossed poles laced with barbed wire, in the gen-eral shape of an hour glass, b. A beach obstacle,usually made of steel bars, channel iron, or thelike, imbedded in concrete and used to interferewith beach landings. 2. A concentration of troopssecurely entrenched or fortified, with arms and

defenses facing all directions. 3. Navy. A small,mortarlike, antisubmarine projectile.

hedgehop, v. Slang, intr. 1. To fly close to theground, rising up over hedges, trees, houses, orother obstacles as they present themselves. 2.In a less exact sense, to fly at a very low level.

Hence, hedgehopping, n.hedgehopper, n. Slang. 1. A small, light airplane,

esp. one of the cub type. 2. One who hedgehops.3. A hedgehopping flight,

hedgehopping bombing. Bombing from a verylow altitude. Popular.

heel, Vi intr. Of aircraft: To tilt sideways, as in abank. Usually with over.

heeling error. An error in the indication of anaircraft's magnetic compass, caused by a tiltingof the indicator when the aircraft is flying on aneasterly or westerly heading and is not in anormal flight attitude.

See compass error, sense i and note.HEI (auth abbr). 'High explosive incendiary/height, n. 1. The vertical dimension of an object,

i.e., the distance between its topmost surface andits base. 2. Altitude, esp. in reference to an ob-ject in the air above the surface. See altitude, n.,esp. sense i.

height finder. Radar. Any radar set that measuresand determines the height of an airborne object.

height overlay. An overlay showing the heightsof all buildings within a given area.

height-range indicator. Any radarscope thatgives the height and range of a target.

Ileinkel, n. (He) The name of a German airplane-manufacturing company producing planes priorto, and during, WW II, as used in the designa-tions of aircraft.

Heinkel airplanes of WW II included the Ileinkel in,a twin-engine airplane designed as a heavy bomber butused also as a torpedo-bomber, transport, and glider tug;the Heinkel ITJ, a single-engine, low-wing fighter; theHeinkel us, a twin-engine, low-wing float plane used forreconnaissance, torpedo-bombing, or mine-laying; theHeinkel 162, a turbojet lighter in operational use at theend of the war; and the Heinkel 177, designed as a high-altitude bomber, but used also for reconnaissance, mine-laying, and other duties.

Heinkel 178. A German-built, high-wing, jet-propelled monoplane, powered by a turbojetunit, test-flown 27 August 1939.

The He 178 was the first jet-powered aircraft to fly.Its engine, the S 3, developed a thrust of about 1,000pounds. Cf. Whittle engine.

hel (auth abbr). 'Helicopter.'Helen, n. A name given by the Allies to the twin-

engined Nakajima Ki 49.helical scan. A kind of radar scan in which a given

point on a radar beam traces a helical path inspace. Hence, helical scanning.

In helical scanning, the transmitting antenna revolvesabout its vertical axis while changing its angle of elevation.

helicopter, n. (hel) A kind of airplane that derives

lift from revolving wings or blades engine-drivenabout an approximately vertical axis.

A helicopter does not have conventional fixed wings,nor in any but some earlier models is it provided with aconventional propeller, forward thrust as well as lift beingfurnished by the rotor. The powered rotor blades alsoenable the machine to hover, and to land and take offvertically. Cf. autogiro, n., and see II (abbr), sense 2.

Attrib., as in helicopter maintenance, pilot, rotor, etc.helicoptere, n. [French.] The unanglicized word

for 'helicopter/ sometimes found in early Eng-lish-language contexts on aviation.

helicopter tower. A ground-based structure onwhich helicopter rotors are mounted for testing.

heliport, 11. An airport set up specially for heli-copters.

A heliport is of much smaller dimensions than a con-ventional airport, and can easily be located in a restrictedplace, as on the roof of a building.

helium, n. A lighter-than-air, nonflammablegaseous element, inert and colorless, having anatomic number of 2, and an atomic weight of4.003. He (symbol).

Helium is often used as the lifting gas in balloons andairships, and is transmuted from heavy hydrogen in theexplosion of a hydrogen bomb.

hell bomb. An emotional term for 'hydrogenbomb/

Hellcat, n. A popular name for the F6F.Helldiver, n. A popular name for the A-25, the

SB2C, and the SBF.helm cloud. A helmet cloud.helmet, n. Any special piece of headgear designed

to protect the wearer from shell fragments, crashinjury, cold, etc., usually made of steel or leatherand lined or padded.

See crash helmet, flying helmet.helmet cloud. A crest cloud. A local name in

certain parts of England. Also called 'helm cloud.'helper, n. Specif. The initial and unskilled posi-

tion in a given AF Specialty; a person fillingsuch a position.

helping wind. A wind blowing from such directionas to advance the groundspeed of a given air-craft.

IlelRec (auth abbr). 'Health record.'hemohyperoxia, n. Medicine. Hyperoxia of the

blood.hemohypoxia, n. Medicine. Hypoxia of the blood.hemopleonexia, n. Medicine. A condition aris-

ing when the hemoglobin gives off less oxygen tothe tissues than normally.

Hendon KAF Station. An RAF air field some 8miles northwest of London, formerly noted for itsannual air show. Also called /RAF Station,Hendon/

H engine. An internal-combustion, piston enginehaving two rows of vertically-opposed cylinderson each side of the engine, driving two separate

crankshafts geared to a common central shaft.The Rolls-Royce Eagle engine is an H engine.

Henschel, n. (Hs) The name of a German com-pany producing airplanes, aerial weapons, andantiaircraft weapons during WW II.

Some well-known IIenschel airplanes used in WW IIincluded the IIenschel 123, a biplane dive bomber; theHenschel 126, a high-wing monoplane developed primarilyfor reconnaissance, artillery spotting, etc.; and the Hen-schel I2Q, a twin-engine, low-wing monoplane for groundattack.

Henschel weapons included the IIenschel 293, 2Q4, 295,etc., air-to-air and air-to-surface radio-controlled rocketbombs.

herdet (auth abbr). 'Hereby detached from dutyassigned and from such other duty as may havebeen assigned/

Herman Nelson heater. A portable hot-air heaterusing gasoline, used esp. for warming aircraftengines.

Hermes, n. A post-WW II Handley-Page civiltransport airplane, developed from the Hastings.

Heron, n. [It. Airdne.] A popular name for theItalian Cant Z.506B.

hershey bar. [After Maj Gen Lewis B. Hershey(1893- ).] An overseas bar. Slang.

hessian, n. A coarse, burlap-type cloth of hemp orhemp and jute. See prefabricated bituminoussurface.

heterodyne frequency. Electronics. A separatefrequency produced by the combining of twodifferent frequencies, equal either to the differ-ence between, or the sum of, the original twofrequencies. Cf. beat frequency.

HF (abbr). 1. auth. 'High frequency.' 2. Heightfinding/Also H/F (abbr).

H.F. (abbr). 'High-altitude fighter/ British.HF/DF (abbr). 'High frequency direction finding/HFORL (abbr). 'Human Factors Operation Re-

search Laboratory/The HFORL at Boiling AFB succeeded the HRRL,

See human resources research.Hg (symbol). A symbol for mercury.HH (code). The US Naval designation for rotary-

wing air-sea-rescue aircraft.hhg (auth abbr). 'Household goods/hhld (abbr). 'Household/H-hour, n. A term customarily used to refer to the

hour at which some specified operation will be-gin, as an attack, amphibious assault, or move-ment.

Hickam Air Force Base. An AF base at Hono-lulu, Oahu Island, named for Lieutenant ColonelHorace Meek Hickam, who died in a plane crashin 1934.

high, n. Meteorology. 1. An area or region of highatmospheric pressure. 2. A peak in a constant-pressure surface.

high, a. 1. Of an airplane, element, squadron, etc.:

Above other airplanes, elements, or squadrons ina formation. 2. Above the horizontal plane ex-tending out from an aircraft, as in the phrase,'twelve o'clock high/ See clock, n.

bigb altitude. (HA) An altitude considered to berelatively high.

'High altitude' is sometimes given precise meaning(see altitude, n., note), but it generally means any alti-tude at which height constitutes a special problem, as inoperating aircraft or other equipment, in carrying outmilitary operations in the air, in adapting to the rarefiedatmosphere, to the cold, or other phenomena peculiar tohigh altitudes, or in observing objects on the ground.

As an attrib., 'high altitude' is used to designate (1) anaction, operation, or performance carried out at a highaltitude, as in high-altitude acrobatics, flight, interception,test, mission, etc.; or (2) equipment designed for use athigh altitudes, as in high-altitude aircrajt rocket, bomber,clothing, engine, etc.

high-altitude bombing. Specif. Bombing, esp.horizontal bombing, from a high altitude, suchas from an altitude of over 15,000 feet. See alti-tude, ., note.

high-altitude foxhole. A fanciful name for theP-38 or other high-altitude fighter of WW II.

high-angle fire. Gunfire from a weapon set at anelevation angle greater than that for maximumhorizontal range. See range, n., sense 6.

high-angle gun. A cannon such as an antiaircraftcannon, capable of firing at a high angle of ele-vation.

high-angle strafing. Strafing from an airplane ata comparatively high dive angle, e.g., of approx-imately forty-five degrees.

high aspect ratio. An aspect ratio considered rela-tively high. Said of a long, narrow airfoil.

high blower. A setting on certain internal super-chargers for the supercharger to run at its highestrotational speed; such a supercharger running atits highest rotational speed.

high capacity bomb. An explosive bomb de-signed to produce maximum blast, with acharge/weight ratio of more than 70 percent.British.

high command. A term applied to the highestcommand echelon of a military or naval estab-lishment, service, or field force.

high cover. Cover provided by airplanes at highaltitude, esp. distinguished from that providedby airplanes at a lower altitude; the airplanesproviding such cover. See cover, w., sense 2.

higher, a. Specif. Above another in a chain of com-mand, as in higher authority, higher echelon,higher headquarters.

high explosive. (HE) Any powerful, nonatoinic ex-plosive characterized by extremely rapid detona-tion and having a powerful disruptive or shatter-ing effect. Distinguished from a low explosive.

high-explosive bomb. Any aerial bomb charged

with a high explosive; specif., any such bombchiefly dependent upon only its explosion, orblast efiect, to create damage.

'High-explosive bomb,' in its broader sense, is a genericterm encompassing armor-piercing bombs, general-purposebombs, light-case bombs, and semi&rmor-piercing bombs.A high-explosive bomb is distinguished from a chemicalbomb or atomic bomb, and in its specific sense, from afragmentation bomb.

high fidelity. As defined in specific AF context,the fidelity of a radio receiver for reproducingaudio frequencies of from 50 to 10,000 cycles persecond without serious distortion. Said of an am-plifier, radio-receiving set, or the like.

The human voice has a frequency range of at least 60to 10,000 cycles per second.

high frequency. (HF) Any radio frequency be-tween 3,000 and 30,000 kilocycles.

In combinations, as in high-frequency control channel,high-frequency direction finding, high-frequency radio,high-frequency resistance, etc.

high latitude. Any latitude considered high innumber, approaching either pole.

high level. 1. A high altitude (which see). 2. Ahigh level of command.

Attributive uses: In sense 1, as in high-level attack,bomber, flyingf etc.; in sense 2, as in high-leval decision,staff, etc.

high-level bombing. High-altitude bombing.high-lift blade. A rotor blade designed to give

greater lift than a commonly-used blade.high-lift device. Any device, as a flap, attached to,

or built into, a wing to increase lift.high-oblique photograph. An oblique aerial

photograph taken at such an angle that the hori-zon is shown.

high octane. Short for 'high-octane fuel.1high-octane fuel. A gasoline containing a rela-

tively high percentage of octane, hence possess-ing good antiknock qualities.

high-order detonation. Complete and especiallyrapid detonation.

high pitch. The pitch of a propeller blade set at ahigh blade angle other than the feathering angle;specif., on a controllable-pitch propeller, thepitch at its maximum blade angle other than thefeathering angle.

A propeller blade at high pitch takes a greater bite ofair than at low pitch; consequently high pitch producesmore thrust at a given rpm than low pitch.

high-pressure area. Meteorology. A region of highatmospheric pressure.

high-pressure oxygen equipment. A kind ofaircraft oxygen equipment designed to withstanda relatively high internal gas pressure.

High pressure oxygen equipment is made to withstandas much as 1,800 pounds pressure per square inch, andwill function efficiently at pressures as low as 200 pounds.

high-pressure test cartridge. A cartridge con-taining a heavier bullet than normal and an ex-cessive propelling charge, used in proof-testing afirearm.

High-pressure test cartridges develop pressures approxi-mately 20% higher than those of ordinary cartridges.

high priority. A priority of a high order of prece-dence.

Attrib., as in high-priority target, a target demandingattention before other targets.

high reconnaissance. Aerial reconnaissance froma high altitude.

high rudder. Top rudder.high side pass. A pass from above toward the side

of an aerial target.high speed. A fast speed.

'High speed' is an indefinite term, but as applied toaircraft, it often means any speed at which special prob-lems arise, as in aerodynamics, navigation, or gunnery.

In combinations, as in high-speed aircraft, high-speeddive, high-speed reconnaissance, high-speed refueling, high-speed target, etc.

high-speed stall. A stall occurring when thespeed becomes so great as to induce the wing orother airfoil into a critical angle of attack, result-ing in turbulent separation.

hightail, v. To hightail it, to run or fly away fast;to clear out. Slang.

high-test fuel. A fuel, like high-octane fuel, thatgives good performance.

high velocity. Fast velocity. Said esp. of bullets,rockets, or other projectiles.

In Army usage, high velocity for small-arms projectilesis considered to be between 3,500 and 5,000 feet per second.

high-velocity aircraft rocket. (HVAR) Anylarge air-to-ground aircraft rocket specially de-signed for high velocities, esp. such a rocket (sixfeet in length) developed by the US during WWII. Nicknamed 'Holy Moses/

The HVAR was first used operationally in July 1944.high wing. A monoplane wing attached at or near

the top of the fuselage. Used attrib., as in high-wing bomber.

high-wing monoplane. Any monoplane havingits wing mounted at or near the top of, or above,the fuselage.

A monoplane having its wing mounted above the fuse-lage is sometimes called a 'parasol monoplane,' and is thendistinguished from other high-wing types.

Hill Air Force Base. An AF base in Ogden, Utah,named for Major Ployer P. Hill, killed in 1935.

Hillcr, n. [Hiller Helicopters, Inc., US firm.] Usedin the names of helicopters.

Hiller JH-2 Hornet, a two seat helicopter driven byramjets at the blade tips; Hiller UH-12B, an ambulancehelicopter. See H-23A, II-23B, HTE-2

Ilindenburg, n. A large rigid airship built by theGermans. Also known as the 'L.Z. 129.'

The Hindenburg was commissioned in 1936 and carriedmore than 1,000 passengers on ten scheduled round tripsbetween Frankfort, Germany, and the US before thefateful accident of 6 May 1937, when the airship wasdestroyed by fire while landing at Lakehurst, N.J. Theairship displaced 7,063,000 cubic feet, and was adaptedto the use of helium, as well as hydrogen, although heliumwas not available for its use.

hinge axis. An axis about which a control surfaceswings.

hinge line. A line coincident with or marking theaxis about which a control surface swings.

hinge moment, The tendency of an aerodynamicforce to produce motion about the hinge line of acontrol surface.

More technically, the hinge moment is the productof the aerodynamic force acting upon the center of pres-sure of a control surface and the perpendicular distancefrom the center of pressure to the hinge line.

Hiroshima bomb. The atomic fission bombdropped at Hiroshima, Japan, on 6 August 1945,the first atomic bomb to be used against anenemy.

hist (auth abbr). 'History' or 'historical.'histohyperoxia, n. Medicine. Hyperoxia of the

tissues.histohypoxia, n. Medicine. Hypoxia of the tis-

sues.histotoxic anoxia. An oxygen deficiency resulting

from a decrease of oxygen utilization by the tis-sues due to poisoning of the tissue cells.

hit, 11. Specif. 1. A blow or impact on a target by abullet, bomb, or other projectile. 2. An instanceof striking something with a bomb, or the like,as in 'he had two hits and one miss.'

hit, v. In specific senses. 1. To hit and run, to strikethe enemy a sudden blow and leave withoutgiving further battle. 2. In slang usage, a. To hitthe deck, (1) to come down to a low or minimumaltitude; (2) to get out of bed. b. To hit the sack,to go to bed. c. To hit the silk, to bail out or makea parachute jump. d. To hit the panic button, toget excited.

hitch, n. A given period of military service; specif.,a three-year period of service. Slang.

hit probability. The probability of hits beingmade on a target out of a given number of pro-jectiles directed at the target.

HL (code). A US Naval designation, for administra-tive purposes, for four-engine landplane VP andVR type airplanes. See VP (code), VR (code).

hlpr (abbr). 'Helper.'HM (abbr). 'Her Majesty' or 'His Majesty.' Used in

combination in designations of ships, as inHMAS, Her Majesty's Australian Ship.

HMG (auth abbr). 'Heavy machine gun.'HNG (abbr). 'Hawaiian National Guard.'Ho (code or abbr). 1. In air navigation, a code or

symbol for 'observed altitude.' 2. Caps. US Navydesignation for a rotary-wing observation air-craft.

Hoardings (code). A German coastal early-warningradar of WW II, a larger version of Freya. Alsocalled 'Mammut.'

hoarfrost, n. Any white or silvery frost.Hoarfrost is the normal kind of frost.

Hohentwiel (code). A German airborne radar of

WW II for locating ships and submarines. Alsodesignated 'Fug 200.'

HOI (auth abbr). 'Headquarters Office Instruction.'hoick, v. Colloq. 1. tr. To jerk or yank an airplane

around in sudden maneuvers; specif., to put anairplane suddenly into a steep climb. 2. intr. Toengage in this activity. Usually with about oraround.

hold, v. 1. intr. Of an airborne aircraft or personswithin: To wait for instructions to land or pro-ceed along a route, the meanwhile maintaining amore or less constant altitude near a specifiedposition or location. 2. To hold position or tohold station, to maintain the position of an air-craft in a formation. 3, To hold fire, to refrainfrom firing at a target; hold fire, the commandgiven.

holdback, n. A device incorporated in a guncharger for holding the bolt open,

holding and reconsignment point. (HRP) Arail or motor center where cars and trucks aresent and held for future routing, and where carsand trucks are unloaded and the cargo held fortransshipment. Usually called an 'H and Rpoint.'

holding attack. An attack made to contain theenemy, esp. while a major attack is beinglaunched elsewhere.

A holding attack may be made to deceive the enemyas to where a simultaneous major attack is being made,to prevent him from reinforcing the elements opposingthe major attack, or to cause him to make errors in com-mitting his reserves.

holding hospital. The former term for an en-route hospital.

holding pattern. A pattern flown by an aircraftwhile waiting landing instructions. See hold, v.,sense 1.

holding point. A designated point or location inthe vicinity of which an aircraft flies or circleswhen holding.

holding war. A war in which both sides makelittle or no progress.

hold status. In supply usage, the status of an ar-ticle or piece of equipment being held to deter-mine its condition.

hole, n. An air pocket which causes an aircraft todrop, as if into a hole.

hole, v. tr. To shoot holes in an object, such as anaircraft.

Holloman Air Force Base. An AF base at Alama-gordo, New Mexico, formerly known as Alama-gordo Army Air Field, renamed for ColonelGeorge V. Holloman, a guided-missile pioneer,killed in 1946.

hollow charge. A shaped charge.Holophane light. [After Holophane Company,

Inc.] Specif. A highly-directional electric lightsometimes used to signal aircraft, or used tomark routes for aircraft.

Holy Moses. A popular name for the high-velocityaircraft rocket (HVAR) of WW II.

Home, n. The British Isles. Used in the names ofcertain British radar systems. See Chain Home.

home, v. 1. intr. Usually home on or home in on.a. Of aircraft or persons within: To fly towarda radiation-emitting source, esp. a radio trans-mitter, using the radiated waves as a guide, b. Ofa guided missile or the like: To direct itself to itstarget by guiding on heat radiations, radarechoes, radio waves, or other phenomena pro-ceeding from, or inhering in, the target. 2. tr.To bring an aircraft to a given spot by radiotransmissions, light beacons, or other signals;also to cause a missile to be directed toward anobject emitting heat, radio waves, or some otherradiation to which the missile reacts.

home base. 1. The base where stationed. 2. Specif.A parent or major base, as distinguished from anauxiliary or satellite base.

home front. The home area, or zone of the in-terior, of a nation at war; specif., the civilianindustries and activities of a country forming apart of the entire war effort.

home office. Specif. The principal office desig-nated by the governing body of a contractor'sfirm, which functions as the directing office of thefirm.

homer, n. 1. A kind of ground-based direction-finding station that utilizes radio transmissionsfrom airborne aircraft to determine their bearingand guides the aircraft usually toward the sta-tion by means of voice communication. 2. A hom-ing beacon (sense i). 3. A homing adapter.

homing, n. 1. The action of the verb 'home.'2. Attrib., as in homing aid, homing antenna,homing beam, and homing signal.

The homing of a missile may be active, semiactive, orpassive. If active, the missile is both the originator andreceiver of radar signals, and as such is subject both todetection and to jamming by window or tinsel. If semi-active, the missile uses a radar receiver to pick up thetarget from echoes of pulses sent out by a cooperatingground facility; in which case, the missile's guidancesystem is subject to jamming but not readily to detection.If passive, the missile depends only on radiation from thetarget, such as noise, infrared rays, or electrostatic dis-charge; in which case the missile's guiding system is moreor less resistant to detection.

homing, a. Of an aircraft or missile: That homes.homing adapter. A device attached to an aircraft

radio receiver for homing the aircraft on a trans-mitting station.

The homing adapter indicates the direction of thetransmitting station with respect to the receiving stationby aural signals, visual signals, or both.

homing beacon. 1. A kind of radio beacon, either

airborne or on the ground, that homes, or gives abearing to, an aircraft equipped with either aradio compass or a homing adapter. See homer,n., sense 2, splasher beacon. 2. Any radar,radio or light beacon that an aircraft uses forhoming. See radar beacon, note.

In sense 1, a homing beacon may be part of a radiorange or it may be a separate installation. See Adcockantenna, note.

homing device. 1. Any transmitter, receiver, oradapter used for homing aircraft, or used by air-craft for homing purposes; a homer. 2. Any de-vice incorporated in a guided missile or the liketo home it on a target.

In sense 2, such a device utilizes light waves, radiowaves, heat waves, etc. See home, v., sense ib. In thecase of a moving target, a homing device may be designedeither to maintain a steady pursuit course directly towardthe target, or to maintain a lead angle while interceptingon a collision course.

homing guidance. The guidance given a guidedmissile or the like by built-in homing devices.

homing range. Specif. The maximum distanceat which a homing device incorporated into anair vehicle becomes effective in respect to atarget or to a homing station.

homing station. A station at which a beaconemits signals that may be used for homing.

homogeneous armor. An alloy-steel armor, heat-treated for uniform hardness throughout. Cf.face-hardened armor.

homogeneous assignment. The assignment ofrelated or similar functions or duties to an in-dividual or group of individuals in accordancewith their skills and capabilities.

homogeneous grouping. The grouping togetherof related or similar functions, jobs, or dutieswithin an organization; a group of similar func-tions, etc. resulting from this action.

hon (auth abbr), 4HOnOr/ 'honorable,' or 'honor-ably.'

honcho, n. [Japanese.] The boss. Jocular. Hence,honcho, v., to boss a job.

honeycomb, n. A grid used in certain wind tun-nels to straighten airflow.

Hono {auth abbr). 'Honolulu.'honorable discharge. (HD) The separation of an

officer or enlisted person from the Armed Forceswho has met the conditions set forth by regula-tions as to efficiency or honorable and faithfulservice; a certificate testifying to such a dis-charge. See discharge, ., separation, n.

Honorary Air Reserve. Formerly, that part ofthe reserve components of the AF consisting ofretired personnel with honorable service. Nowhist.

Persons in the HAR are now in the Retired Reserve(which see).

honor flight. A formation of airmen that partici-

pates in the ceremony honoring a very importantdignitary upon his arrival or departure from anAF establishment.

The honor flight is of different sizes according to theimportance of the dignitary. The President warrants21 airmen. This flight forms into two lines facing eachother to make an aisle down which the dignitary walksor marches. See Presidential salute.

honor guard. A specially chosen guard detailed toescort a distinguished person, or one detailed toescort a deceased person at a military funeral.

hood, n. 1. A covering for some part of an aircraft.See engine cowling. 2. Specif, a. A cockpitcanopy, b. Any opaque covering placed over allor part of a cockpit for practicing instrumentflying. Hence, to fly under the hood.

hooded flight. A flight in which the pilot is underan opaque hood, simulating instrument-flyingconditions.

hook, n. Specif. An arresting hook.hookup, n. In air refueling, a juncture between

the fuel hose of a tanker aircraft and the air-craft being refueled. See wet hookup.

hop, n. 1. The flight of an aircraft between takeoffand landing: See note. Colloq. 2. Electronics. Theexcursion or movement of a radio wave from apoint of origin, or point of reflection, to theionosphere and back to earth.

In sense i, a hop is usually between two different points,but it may begin and end at the same point, as in certaintest hops.

hop, v. In slang usage. 1. tr. To attack an aircraftfrom the air. 2. tr. To take a person on a hop.3. intr. To fly on a hop. 4. To hop of, to take off.5. intr. To lift an airplane for a brief moment offthe ground while making a practice run. Hist,Used in reference to a ground maneuver in theearly days of flying.

hopper, 11. Specif. A separate compartment withinan aircraft engine's oil tank, from which, duringwarmup, the engine draws its oil. Also called a'hotwell.'

Hoppi-eopter, n. [Hoppi-copters} Inc., an Ameri-can helicopter-manufacturing firm.] Used in thenames of certain small, light helicopters, as Hop-pi-copter Model ioif Hoppi-copter Model iO2} etc.

The first Hoppi-copter, built in 1945, was designed to bestrapped to a person's back.

HOR {auth abbr). 'Home of record.7horiz {auth abbr). 'Horizontal/horizon, n. 1. The line formed by the apparent

meeting of the earth and sky as observed fromany point. 2. A plane that runs through the eyeof an observer, or a plane parallel to that plane,at right angles to the vertical. 3. A line that in-dicates such a plane on a flight instrument, as inthe artificial horizon.

The horizon (in sense 1) is sometimes spoken of as the'apparent horizon,' 'natural horizon,' 'visible horizon,'etc., esp. to distinguish it from a horizon in sense 2, which

may refer to a bubble horizon, celestial horizon, rationalhorizon, or sensible horizon. See separate entries.

horizontal, n. (horiz) A horizontal plane or line,as in 'in the horizontal/

horizontal, a. (horiz) 1. a. Parallel to the earth'ssurface considered as a smooth and uniformsphere, b. Parallel to the sensible horizon. 2. Ofan airfoil: Attached so that it lies perpendicular,or nearly so, to an aircraft's plane of symmetry,and in a plane parallel, or nearly parallel, to thelongitudinal axis. Said of a fin, stabilizer, etc.3. Of a motion or a resultant of motion: Done in ahorizontal plane; lying within a horizontal plane.4. Of an organizational structure: Adapted toprovide control by a commander or supervisorwithout dependence upon subordinate command-ers or supervisors. Cf. vertical, a.

Hence, horizontally, adv., in all senses.horizontal attitude. An attitude of an aircraft in

which the horizontal axes are in a plane at rightangles to a plumb line.

horizontal axis. 1. Either the lateral or the longi-tudinal axis of an airplane. Usually pi. in refer-ence to both. 2. In a gyroscope or gyroscopicbody, an axis of precession that lies more or lesshorizontal.

horizontal bomber. A bomber designed to dropbombs while flying horizontally, as distinguishedesp. from a dive bomber.

horizontal bombing. Bombing from an airplanein horizontal flight, as distinguished from divebombing, glide bombing, toss bombing, etc. Alsocalled 'level bombing.'

horizontal fin. Any fin mounted horizontally(sense 2) on an airship and extending outwardon one side only, to which an elevator is at-tached. Sometimes called a 'horizontal stabilizer.*

The term 'horizontal fin' is not commonly applied to acorresponding part on an airplane. See horizontal stabi-lizer, senses 1,2, and note.

horizontal flight. A flight in which the aircraftmaintains a uniform altitude above sea level.

With a helicopter, horizontal flight can be accomplishedin a forward, sideward, or rearward direction.

horizontal line. 1. A line of uniform altitudeabove sea level at all its points. 2. A line parallelto the sensible horizon.

For short distances, a horizontal line (sense 1) may beconsidered to be in a single plane, at right angles to aplumb line directed to the earth's center of gravity.

horizontal plane. 1. Any plane that has uniformaltitude above sea level at all points. 2. A projec-tion of all the horizontal planes into a singleplane as seen from above or below.

Strictly speaking, this plane (sense 1) is not a planesince it follows the curvature of the earth, but for practicalpurposes it is such. In sense 2, the term is used in suchlocutions as 'movement in the horizontal plane/ i.e.,movement at right angles to the vertical. See verticalplane, note.

horizontal range. The distance measured hori-zontally between a gun and its target; specify inantiaircraft gunnery, the distance between a gunand a spot on the ground directly beneath thetarget. See range, n., sense 6, and note.

horizontal rudder. A term used by WilburWright for a control surface projecting forwardof the wings, used for longitudinal balancingand steering in the manner of an elevator andhorizontal stabilizer.

horizontal stabilizer. 1. The horizontal compo-nent of an airplane's empennage extending onboth sides of the fuselage or boom (as in a twin-boom tail): See note. 2. Also applied to a part ofthis component on only one side of the fuselage.Hence, the plural form 'horizontal stabilizers'and hence, references to the right or left hori-zontal stabilizer. 3. Sometimes applied to thehorizontal fin of an aerostat. See horizontal fin.

Strictly speaking in sense i, the horizontal stabilizerdoes not include the elevator or elevators, but where thedistinction is not important the term is used to includethem, as in 'the left horizontal stabilizer was shot off.'The horizontal stabilizer affords the airplane longitudinalstability. See tailplnnc, n.

horizontal tail. The complete horizontal com-ponent of an aircraft's empennage, esp. of anairplane's empennage, consisting of both fixed(or adjustable) and movable surfaces.

horizontal tail area. The area of an aircraft'shorizontal tail.

In measuring the horizontal tail area, it is customaryto include also the projected area taken through thefuselage or other component upon which the tail ismounted, and to discount the extra area of any fairingsor fillets.

horizontal tail surface. 1. Any of the surfaces orairfoils of the horizontal tail. 2. Usually pi. All ofthe surfaces or airfoils comprising the horizontaltail.

horizontal target complex. An industrial targetcomplex consisting of potential targets related bytheir being in the same industry, as, for example,a complex of oil refineries. See target complex.

horizon-to-horizon camera. A trimetrogoncamera.

horn, n. 1. A device for making a warning noise, asused, for example, in a landing-gear warning sys-tem. 2. A short lever attached to a control sur-face, to which the control cable or other operat-ing line or rod is attached. See note. 3.Electronics.A horn-shaped radiator sometimes used at theend of a wave guide or other transmission line todirect radiation in a special pattern. See radi-ator, n., sense 2a. 4. A telephone. Slang.

In sense 2, 'horn' is often distinguished by a modifiersignifying the control surface to which it is attached, as inelevator horn, rudder horn, etc.

horn antenna. A radar antenna assembly ter-minating in a horn (which see, sense 3), from

which radar waves are radiated directly intospace without benefit of a reflector.

Hornet, n. A British twin-engine, single-seat,long-range fighter developed by de Haviliandlate in WW II.

horn feed. A radar feed in the shape of a horn. Seefeed, n., sense 1.

horn radiator. A horn or a horn antenna.Horsa, n. A British all-wood, transport glider of

WW II, developed by Airspeed.horse, n. One horsepower. Slang.horse, v. In slang usage. 1. To horse the controls, to

yank savagely on the controls of an airplane. 2.To horse an airplane, to jerk an airplane about inflight. 3. To horse around, to fly an airplanewithout regard to usual patterns or discipline.

horsefly, n. [Orig. a code name.] A forward aircontroller airborne in a liaison-type aircraft.

Attrib., as in horsefly mission, an aerial mission flownby a forward air controller. Cf. Mosquito, n., sense 2.

horsepower, n. (hp) Construed either as sing, orpi. A power equal to the force necessary to raise33,000 pounds one foot in one minute against thepull of gravity; a unit of measure representingthis power; specif., brake horsepower.

Horsepower is used esp. in measuring the power outputof an internal-combustion reciprocating engine, cr of aturboprop engine. Cf. thrust, n., sense 1. and see brakehorsepower, friction horsepower, indicated horse-power, rated horsepower, thrust horsepower.

Horten Ho 9. An experimental jet fighter of theflying-wing type being developed in Germany byHorten Brothers at the end of WW II.

hosepipe, v. intr. To stream forward, or squirt, asfrom a water hose. Said of fire from an automaticweapon.

hosp (auth abbr). 'Hospital.'hospital, n. (hosp) A facility for the care of the

sick and wounded.This term is now used without a modifying attrib. See

general hospital.hospital aircraft. An aircraft furnished as a hos-

pital for the accommodation of patients en route.hostile, n. Specif. An enemy aircraft.hostile, a. 1. Belonging to, or sent forth by, the

enemy. 2. Inimical, unfriendly. See friend, n.tneutral, n.

In combinations, as hostile air, hostile aircraft, hostileair force, hostile flak, hostile territory, etc.

hostile act. An act that is interpreted as hostileor is intended to be hostile.

Recognition of a hostile act requires judgment, butcertain criteria may be set up for guidance. For example,radar jamming without previous arrangement, or a low-level approach in airspace prohibited to friendly aircraft,or flare-dropping at night in friendly territory.

hostile maneuver. Specif. An aerial maneuver in-dicating hostile intentions.

hostility, n. 1. pi. Acts of battle or of fighting; actsof warfare. 2. Usually pi. The state or situation

under which armed conflict takes place or can beexpected to take place.

Hostilities (in sense i) may begin or cease withoutreference to the beginning or end of a war. For usage insense 2, see sneak, n.

hot, a. In slang usage. 1. Of an airplane: Fast;capable of high speed. 2. Of a pilot, esp. a fighterpilot: a. Skillful or expert, b . Reckless; preten-tious; conceited as to his own ability. 3. Radio-active, esp. highly radioactive. 4. Of information,papers, messages, etc.: Urgent; extremely im-portant; having a high security classification.

hot, adv. In a fast manner. Slang.hot-air balloon. A fire balloon.Hotel (code). An authorized word for the letter 'H.'

See Alfa (code).hot line. A communication channel providing in-

stantaneous communication without switching.hot papa. An asbestos-clothed crew member on an

aircraft carrier whose duty is rescuing personsfrom any burning aircraft on the carrier's flightdeck. Colloq.

hot rock. In slang usage. 1, A hot pilot. 2. A skill-ful, industrious person.

hot seat. An ejection seat. Slang.hot spot. 1. A spot or place of intense heat, as in a

jet engine. 2. A region of intense antiaircraft fire.Slang. 3. Photog. A spot on a photograph causedby excessive light. Slang.

hot s tar t . The starting of a jet engine in such amanner as to cause the engine to exceed its nor-mal operating temperature.

hot target. An important target, or a target re-quiring immediate attack. Slang.

hot war. A war of open armed conflict. Distin-guished from 'cold war.'

hotwell, n. A hopper.hour, n. (hr) 1. A measure of sixty minutes in

passing time; specif., a flying hour, as in 'helogged 400 hours.' 2. A measure of distance interms of flying time, as in 'New York is less thanfive hours from London.'

hour angle. The angular distance between twogiven hour circles on the celestial sphere; specif.,the local hour angle.

See Greenwich hour angle, local hour angle* side-real hour angle.

hour circle. Any great circle on the celestialsphere passing through both celestial poles,used as a line of angular distance or of timemeasured eastward between the vernal equinoxand any given celestial body through which agiven hour circle passes. See right ascension.

An hour circle is not a projection of a particular meridianon the earth, because the hour circle moves with themovement of the body. The meridian is fixed.

housekeeping, n. (hskpg) The activity at an in-stallation dealing with such functions as food

service, housing, payment of personnel, records,and administration.

At any installation, two kinds of responsibilities arepresent. The first, which has nothing to do with house-keeping, is that of carrying out the assigned mission interms of overall operations; the second is that of takingcare of wants and needs of personnel at the installation.'Housekeeping' is the term applied to the activity con-nected with the latter. At larger installations, specialunits are usually established to take care of housekeeping.See housekeeping unit.

housekeeping equipment . In supply usage, thatequipment listed in a table of allowance, requiredfor the shelter, health, welfare, and administra-tion of personnel.

housekeeping uni t . At certain installations, usu-ally large, a unit specially organized to do thehousekeeping for all the activities stationed atthe installation.

This unit may be on a squadron, group, or wing level.See air base group, air base wing, base support,wing, ., sense 11 and note.

hover, v. intr. 1. Of any aircraft: To fly back andforth or circle over a given spot or object. 2. Of ahelicopter or dirigible: To remain in a stationaryposition at a given altitude above the surface.

A helicopter is said to hover (sense 2) when it maintainsitself in the air at zero translational velocity and zerovertical velocity in relation to the air.

hovering, n. The action of the verb 'hover/ esp.in sense 2. Attrib., as in hovering attitude, hoveringflight, etc.

hovering, a. Of an aircraft: That hovers.hovering ceiling. The maximum altitude at which

a helicopter can hover under a given set of condi-tions.

How (code). A word formerly authorized for theletter 'H.' See Able (code).

how (auth abbr). 'Howitzer.'Howell Commission. The Federal Aviation

Commission, named for its chairman, ClarkHowell (1863-i 936), editor of the Atlanta Con-stitution. Hist.

howgozit, n. ['How goes it.'] A graph sometimeskept aboard an airplane, indicating fuel con-sumption and distance flown.

howitzer, n. (how) A cannon with a relativelyshort barrel, designed for high-angle fire againsttargets that cannot be reached by flat trajec-tories.

howler, n. An audio device for warning an operatorthat signals are appearing on a radar screen.

ILP. (abbr). 1. 'Handley Page.' 2. 'Hot pilot.'Up (code). 'Pressure altitude.'hp (auth abbr). 'Horsepower.'HPF (abbr). 'Highest probable frequency/HPT (abbr). 'High-pressure test.'

Used esp. in combinations, as in HPT ammunition,IJPT cartridge.

hq (auth abbr). 'Headquarters.'

HR (code). The US Naval designation for rotary-wing transport aircraft.

hr (auth abbr). 'Hour.'HRI (abbr). 'Height-range indicator.*HRP (auth abbr). 'Holding and reconsignment

point.'HRRC (abbr). 'Human Resources Research Cen-

ter.' Now hist.HRRI (abbr). 'Human Resources Research Insti-

tute.' Now hist.HRRL (abbr). 'Human Resources Research Labo-

ratory.' Now hist.HRS (auth abbr). 'Honorary Reserve Section.'HS (code). The XJS Naval designation, for adminis-

trative purposes, for four-engine seaplane VP andVR type airplanes. See VP (code)7 VR (code).

Hs (abbr). 'Henschel.'Hs (code). In air navigation, a code or symbol for

'sextant altitude/hs (auth abbr). 1. 'Hardstanding.' 2. Caps. 'High

school.'H-scan, n. 1. A scan for presentation on an H-

scope. 2. An H-scope. Popular.H-scope, n. A modified version of the B-scope.hsg (auth abbr). 'Housing.'hskpg (auth abbr). 'Housekeeping.'H-system, n. A radar navigational system by

which an aircraft fix is obtained by airborneequipment which establishes the direction of, andmeasures the distances from, two radar beaconson the ground.

The principal H-systems used are the Gee-H, Micro-II,Rebecca-H, and Shoran. See II {letter),

HT (code). A US Naval designation for rotary-wingtraining aircraft.

ht (abbr). 1. 'Heat.' 2. 'Height.'HTA (auth abbr). 'Heavier than air.'HTE-2. The US Navy version of the H-23A, pro-

vided with a four-wheel landing gear.htrac (auth abbr). 'Half-track.'htrk (abbr). 'Half-track.'H-type engine. An H engine.HU (code). A US Naval designation for rotary-wing

utility aircraft.hub, n. Specif. A propeller hub or a rotor hub. See

separate entries.hub cannon. A cannon mounted through a pro-

peller hub.hub dynamometer. An instrument built into the

hub of a propeller attached to an aircraft enginefor measuring thrust, torque, or both.

hub tilting. 1. The tilting of the rotor hub of ahelicopter or autogiro. 2. A method of controllingthe rotor of a helicopter or autogiro by tiltingthe rotor hub as the means of tilting the rotor.Cf. cyclic pitch control, direct control.

Hub tilting is chiefly limited to autogiros and to heli-copters with jet-driven rotors.

Hudson, n. A popular name for the A-29.Hughes flying boat. A giant, eight-engine, all-

wood, experimental flying boat built by theHughes Aircraft Company.

The Hughes flying boat has a 320-foot span comparedwith a 230-foot span of the B-36. It has been test-flownbut not put into service.

IIuk (auth abbr). 'Hunter-killer.' Attrib., as in Hukoperation.

hull, n. 1. The frame or body of a thing built tomove on or pass through water, as that of a vesselor the boatlike structure of a flying boat's fuse-lage. 2. trans}, a. An airship hull (which see), b .The outer casing of a rocket, guided missile, orthe like.

hull displacement. The amount of water, byvolume or by weight, displaced by the hull of aflying boat.

human resources research. Research in suchfields as sociology, psychology, and demographywith the object of discovering and using humanresources, together with material resources, forthe achievement of national objectives.

This phrase has been used in the titles of three AForganizations, all now historical, the Human ResourcesResearch Laboratory formerly at Boiling AFB, the HumanResources Research Center formerly at Lackland AFB,and the Human Resources Research Institute formerlyat Maxwell AFB. See AFPTUC {auth abbr) and HFORL{abbr).

humidity, n. Moisture or dampness in the atmos-phere. See absolute humidity, relative hu-midity.

hump, n. 1. A mountain or chain of mountains;specif, (capitalized), an eastern range of theHimalaya between China and India or Burmaover which air transport missions were frequentlyflown in WW II. Colloq, 2. Any bulge or rising ina line drawn on a graph. See age hump.

hvimp speed. The speed of a seaplane during take-off at which the water resistance is at a maximum.

hums (auth abbr). 'Humanitarian reasons/Hun, n. 1. A derogatory word for a German, used

in WWI and WW II. 2. Personified. The Germannation.

This was a word used for emotional buildup. Oucehostilities were ended, its use subsided.

hun (auth abbr). 'Hundred/hung bomb. A bomb which accidentally remains

hanging to the bomb rack after the releasing ac-tion has been taken.

hunt , v. intr. 1. Of an aircraft, guided missile, orthe like: a. To make weaving motions about itsmedian flight path, as in longitudinal or phugoidoscillation, or to vary in flight speed, as if seekinga new angle of attack, flight path, etc. See note.b. In popular usage, to yaw repeatedly. 2. Of acompass: To deviate or waver constantly. 3. Of

a radar scanner: To oscillate or swing of its ownaccord, due to some flaw in the driving system.4. Of a rotor blade: To oscillate about the draghinge.

In sense i, the weaving or yawing may occur withoutmovement of the control surfaces. Cf. seek, v.

Hunter Air Force Base. An AF base at Savannah,Georgia, named for Major General Frank O5D.Hunter (Ret.), a WW I ace, and recipient of theDistinguished Service Cross, four clusters.

hunter-killer operation. A coordinated air andsea operation for seeking out and destroying anenemy submarine or submarines.

hunting, n. The action of the verb 'hunt.'hunting motion. S,pecif. Lagging motion.Hurribomber, n. A Hurricane fighter equipped to

carry bombs.hurricane, n. 1. A violent tropical cyclone, esp.

one in the West Indies, with wind above 75 mph.2. Capitalized. A British low-wing fighter devel-oped by Hawker, used in WW II.

hutment, n. 1. The housing of persons in huts; agroup or camp of huts. 2. Often incorrectly usedfor 'hut.'

HV (aulh abbr). 'High velocity.'hv (aulh abbr). 'Heavy.'HVAP (abbr). 'High velocity armor-piercing.'HVAR (auth abbr). 'High velocity aircraft rocket.'HVAT (abbr). 'High velocity antitank.'hvy (abbr). 'Heavy.' See hv (auth abbr).H-warhead, n. A warhead containing a hydrogen

bomb.hwy (auth abbr). 'Highway/hyd (auth abbr). 'Hydraulic'hydraulic, a. (hyd) Specif. 1. Designating mecha-

nisms or devices activated by liquids forcedthrough tubes and orifices under pressure, as inhydraulic brake, hydraulic clutch, hydraulic gunturret. 2. Designating things associated with suchmechanism or devices, as in hydraulic field, hy-draulic line, hydraulic power, hydraulic pressure,hydraulic shop, etc.

hydraulic accumulator, n. A reservoir on an air-plane or other piece of equipment for storing uphydraulic fluid under pressure to serve in emer-gencies as a source of hydraulic pressure.

hydraulics, n. 1. That branch of science or en-gineering concerned with hydraulic systems andmechanisms. 2. Hydraulic mechanisms, or a hy-draulic system.

hydro (auth abbr). 'Hydrographic.'hydroairplane, n. Also hydroaeroplane. 1. A

seaplane, i.e., a float plane or flying boat. 2. Re-strictive. A float plane, as distinguished from aflying boat. Loose usage.

hydrocarbon, n. A compound containing only

hydrogen and carbon, as gasoline, kerosene, orbenzene.

Hydrocol process. A process for extracting andliquefying hydrocarbons from natural gas.

hydrodynamie, a. Pertaining to hydrodynamics.The denotations of this word are parallel to those of

'aerodynamic' (which see, note).hydrodynamics, n. That field of dynamics con-

cerned with the motion and action of water andother liquids, or of the forces acting on bodies inmotion within a liquid.

hydroflap, n. A hydrofoil attached underneath aseaplane near the stern and entering into thewater, used as a brake or rudder.

hydrofoil, n. A foil or surface designed to obtaina reaction, such as support, from the waterthrough which it moves.

hydrogen, n. An element which in its uncombinedstate is a colorless, tasteless, and odorless gas,flammable and lighter than any other known sub-stance.

The symbol of hydrogen is H; its atomic weight is1.0080; its atomic number is 1. The ordinary isotope(H1) consists of a single proton in the nucleus and a singleelectron. Its other isotopes are deuterium (H2) and tritium(H3) used in nuclear fusion.

hydrogen balloon. A balloon inflated with hydro-gen as the lifting agent.

hydrogen bomb. A fusion bomb in which an iso-tope of hydrogen is made to fuse under intenseheat, with a resultant loss of weight and releaseof energy. Also called the 'H-bomb.'

hydrographic chart. A chart showing the fea-tures of a given body of water, as tides, currents,depths, nature of bottom, etc.

hydrographic reconnaissance. The reconnais-sance of an area of water to determine the natureof a given expanse of water and any surroundingshore.

Hydrographic reconnaissance includes determiningthe depths of the water, nature of bottom, beach Gradients,and seeking out reefs, rocks, man-made obstacles, etc.

hydrography, n. 1. a. The study of water bodies,as seas, rivers, lakes, etc. b. The art or science ofmeasuring water bodies, determining their char-acteristics and those of associated land areas, andof charting such bodies and areas. 2. Bodies ofwater, esp. as shown on a map or chart.

hydrology, n. The science treating of the natureand distribution of water, often with special refer-ence to underground water.

hydromatic, a. [Hydr&\\\\ 4* automatic] Per-taining to hydraulically-operating mechanismsthat function automatically.

hydromatic propeller. A hydraulicaliy-operatedconstant-speed propeller.

hydroplane, n. 1. A hydroairplane. 2. A hydrofoildesigned to be supported in water by hydro-

dynamic action. 3. A kind of motorboat equippedwith hydrofoils, so that its support in waterwhile in motion is entirely or chiefly derivedfrom hydrodynamic action. Sometimes called a'hydroplane boat.'

hydroponics, n. [Assonant with 'comics.'] Theart, science, or practice of growing vegetables orother plants in special water solution containingthe necessary nutrients, rather than in soil.

Hydroponics was used to a certain extent in WW IIin the Pacific theater to supply fresh vegetables for themilitary; likewise in Japan after WW II.

hydrostabilizer, n. A sponson on a flying boatused to stabilize it upon the water.

hydrostatic fuze. A bomb fuze that functionsunder the influence of water pressure.

A hydrostatic fuze may be set to explode a bomb at apredetermined depth.

hydrostatics, n. A branch of physics dealing withthe pressure and equilibrium of liquids, or ofbodies immersed in liquids.

hygrometer, n. An instrument for measuring andindicating either the relative humidity or thedew point of the air. See hair hygrometer,psychrometer, n.

hygroscopicity, n. The tendency of a substance toabsorb moisture.

Hygroscopicity is an undesirable quality in gunpowderand explosives.

hypenzymopraxia, n. Medicine, A diminishedfunction of an enzyme system caused by an in-sufficiency in the quantity or quality of its en-zymes, as may occur from the inhalation of apoison gas.

hyper (prefix). [Greek 'over' or 'above the ordi-nary.'] A combining form used esp. in medicalterms denoting 'abnormal excess in some contentor degree.' The opposite of hypo (which see).

hyperbarism, n. Medicine. A disturbed conditionin the body arising from an ambient gas pressureor atmospheric pressure being higher than thepressure within the body tissues, fluids, andcavities, as may occur in a sudden descent froma high to a low altitude.

hyperbolic guidance. The guidance or control ofa guided missile or the like in which the differencein the time delay of radio signals transmitted si-multaneously from two ground stations, arrivingat the missile at different time intervals, controlsthe position of the missile.

This system is based upon the geometric theorem thatthe locus of all points of fixed difference in distance fromtwo base points is a hyperbola.

hyperbolic navigation system. Any system ofradio navigation in which the navigating aircraftreceives synchronized signals from at least threeknown points, as in loran, Gee, or Decca.

In any hyperbolic navigation system, the time differ-ence between signals received from any two stations

determines a line of position in the shape of a hyperbola.Crossing this line of position with another line of positionusing at least one other transmitting station establishes afix.

hypergolic propellant. A rocket propellant thatignites spontaneously upon contact with anoxidizer.

'Hypergolic* is a coined word, the element 'golic' beingobtained from a German code word '(JoIa/ used to referto a series of rocket propellants containing methylaniline,organic amine, pyrol, and certain other compounds.

hyperoxemia, n. Medicine. A condition in whichthe oxygen content of the blood exceeds thatnormally existing at sea level; excessive acidityof the blood.

hyperoxia, n. Medicine. Any excess of the oxygentension in the atmosphere or in an animal bodyabove that normally existing at sea level.

Combining forms are aerohyperoxia, cytohyperoxiayhemohyperoxia, histohyperoxia, and pneumohyperoxia. Seeseparate entries.

hyperoxidation, n. Medicine. Any pathological ornonpathological elevation of oxidation within acell or cells above the usual resting metabolicrate for the species concerned.

hyperoxidosis, n. Medicine. A condition character-ized by pathological increase of the rate of oxida-tion within a cell or cells above the usual basalrate for the species concerned, such oxidationbeing in excess of physiological need.

hyperoxypathy, n. Medicine. A disorder of thebody characterized by pathological changes oftissues, brought on by hyperoxia.

hypersonic, a. Of or pertaining to the speed ofobjects moving at mach five or greater. Cf.supersonic, a.

hypersonics, n. A field of study concerned withbodies that move at mach five or greater.

hypersonic velocity. A velocity of mach five orgreater.

hyperventilation, n. Medicine. Excessive or pro-longed ventilation, as may occur in deep breath-ing or overbreathing.

hypo (prefix). [Greek 'under' or 'less than theordinary.'] Used esp. in medical terms denoting'abnormal deficiency or weakness in extent ordegree.'

hypobarism, n. Medicine. A condition in whichthe gas pressure within the body tissues, fluids,or cavities is greater than the surrounding gasor atmospheric pressure.

hypocapnia, n. Medicine. A deficiency of carbondioxide in the blood, as may be brought on byhyperventilation. Hence, hypocapnic, a. Seealtitude alkalosis.

hypohistodiabatism, n. Medicine. A conditioncharacterized by an inadequate gas diffusion be-tween the blood stream and a cell, caused by a

qualitative or quantitative alteration in theblood-cell barrier.

Hypohistodiabatism may become apparent in high-altitude flying.

hypopnea, n. Medicine. A condition of hypoven-tilation resulting from abnormal shallowness andrapidity of breathing.

hypopneumonism, n. Medicine. A lack of properdiffusion of gas between the blood and lungs,caused by a qualitative or quantitative altera-tion of the gas-blood barrier.

hypothermia, n. Medicine. Subnormal tempera-ture of the body. Hence, hypothermic, a.

hypotrophy, n. A condition of progressive degen-eration and loss of function of certain cells andtissues, brought on by an insufficiency of sub-st