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»'T^ DiaTRIPOT^D jT/Xp/f/A 9^ üNCLASSIFiEn ^thor

I.o- rrd. e*tl "'crk ' rr.y Wavy >rtvit<

author 1 i i- i ^ i

Lab. File 1 1 1 1^1

MalB Office File 1 1 1 1 ^ 1

Chief of Ordnance - 2 2'"'-

TechnicPl Staff - 11*"-

Sprinp.fiold /r^ory - S 1 1 ^

r'aterviiet .'raenal - g 1 \ ^ -

Peek Island Artanal - « i i ^

Prankford Arsenal - 'S i \ i^-—

Pioatlnr.y /Iraanal - I ! l ^ -

■.nerdoen Privinp; OroUnd - g ! 1 *^'

Chiafi Puroau Ordn^noa - * - 1 ^^ -

>Trival QKm Factory - - - 1

ßhlefi Eupanu c^cP _.. i v,elding

^ / / and as *L f P directed

Loctl Circulation ill i as directed

'vailible for special S ß ö 3 1 circulntion.

Other Fttablishnanti • 2 • • raouasting v?ork«

Private Parties payiftg _ _ - - 2 +'or vork«

ÜNCUSSIFJED

iliiiilll WferMf 1/fWW rfffjri Report No. 710/4? Watertcvn Arsenal TT!iy 18, 1935

WCWEI ARMOR »LATE ^CLASSIFIED References: 97th Partial Report of Tent of Thin

Armer Plate, Aberi.eon Proring Oround, ^'o. April 15, 1935«

Watcrtown Arsenal Report *710/SS«

ATpJtrn.üt

This report La a ooanarison of grooved armor olate

anl flat armor olate of eoual weight and the same

oonroosltion and heat treatment. The results uoeJ for

grooved platea arc those taken from P.R. 07, APG.

Those for flat plate were taken from a summary of all

of this tyoe tested at the Proving Ground and covered

in P.R. 1 to 97, APG.

(a) ^he grooved plate is feasible and

economical to roll and heat treat.

(b) It ic from 0^ to 50^ better than an

couivalent weight of the same olate without grooves.

(c) Grooved olate of the name '"eight as

1/^" armor plate successfully withstood the cal, ,210

A.P. Tl (High Vel.) bullet at 100 yds. The Tl

ammunition r,as developed to penetrate 1/-" olate at

800 yds«, or. reported in MinutSQ of the OrJnanco

Comr.ittee «eeting, held Thursday, Way 10th, 1934.

Batiofaotory hcmog^neou" armor nlatc har. bean

Bade for the laat eight /ears of the following oteel

QompoeLtion:

.45/. 55 .40/. 70 /,. 03 /..C? ,16/.96 1.10/1.30 .60/«80*80/«SO

Plates of this oooDOsitlon haTe been heat tröstei by

OUenohlng In Oil from (F700C) 1600oF an.i drawing at

about (^I80c) 11500F - to 410-444 Prinoii hardneafl«

The DOSeibllltlas of increasing ballistic efficiency

by uning a given weight of olate in auch a manner ao to

deflect ani break up bullet coroo, has been Lnvestigated

at this Arocnal during the last two yeara. The results

Obtained are eat forth in W.A. 710/33« The use of a

hard thin front olate of the saae aaterial was found to

help resist penetration In the bottoms of the grooves,

as shown in the above reoort«

Three plateo of the OOBOOSitlMl shown above were

machine-grooved in the annealed condition and then

hardened in the same Banner as flat olate of the same

OOBDOSltion« The tyoes and dimensions of the grooves

are shown in Figures 1, 0, ani 3. These olatos,

designated GHO, GUI, ana (U0, with ani without thin

cover plateS| were tested at the Aber^.ecn Proving Grouni,

Maroh 11 to 14, 193BI The 37th Partial Report of Test

of Thin Armor Plate shows the results obtained. For

convenience these results are umnuvrize-i in Table I.

-8-

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'3*43*

It Lfl evident that th086 OlfttOfl lioplayed greater

balllGtic rerirtanoc than that required In oreGcnt

GDecif Ice.tion • for flat T)latoc of the Jarr.c weight« Ihlfl

oxcenn ballistlo rerl^tance, expressed rs percentage of

the required ballietio limit was ss foiio"ro:

Exceed Required Plate Ballistic Limit by

IIC more than POf

lll(w/o cover olate) 18 1/3^

Gll(w/cover plate) no renult-lack of tejt area

QH?(w/o cover plate) 36 l/?^(average)

HiaCw/oorer plate) PA*?

Hovever, it is well understood that all olatefl

muat exceed the ballietio reouirement and that many of

the olateo tested do sux^ass the reouired limita by a

considerable margin. Therefore, the efficiency of these

grooved plate- should be shown by comparison with actual

re-ults rather than With specified ballistic limits.

Renortfl of Test of Thin Armor ^late from IQ^S to

date are nho,,rn in Partial Reports 1 to 97, Aberdeen

Proving Ground. The earlier results are not comparable

with those now obtained due to differences in range,

ammunition, etc. They '"ill not be included in this study

The great mass of the available data was obtained under

Tent. Speo« 31 vhich recognized a much different

definition of "complete penetratim" than that used at

-4-

present In 8oeo< AXS54. it seems desirabla to inciuie the

oat a thus evellftble but| for this ouroosei Lt will be

necessary to oonvert tho ballistiQ Units of earlier

firings to the substantial eculvalent of those of Soee,

AXu54. Lest -uoh OOnvSrelon rr.ay neem unfair the re rultc

obtained with the grooved elates will be conoarel:

(a) -"ith results of aii firings under Spec«

AX554,-Rev 1., and -Rev. 9%

(b) with reoulte of all firings under like

oondltlons Of rengs and ammunition under SoeO« 31 -

converting figures obtained under Goec. ?.l to ooulvalentc

fer AX854

(o)frlth results of all firings ss in (a) sgalnsc

flat ola^e of the name steel cormoGltlon and heat treatnsnt«

ComioarlGcn (a)

Results available unier AX854 and Its rerlslons are

Btrlotly comoarable with ths result! under connlderatlor

fcr grooved plates« They are suramarlzed for all flat

olates of the thlduiesses Involved In Table II,

-5-

TABLE TI

SuSHS&g of ReaultG of geota Unier AX3S4*

Plpte Thicknesn B>lll<tle .Llji^f - ./.. s... a'

^ea:: of All RtSUltS !'Teen of Rlgbeot lOf of All Reoultr.

s/i«- 1830 an«

7/16" ?180 ■:,46n

l/P" ^PDO 3550

9/16" innuf fie lent 'late

* - From ^prtipl Reoortc of Teet of Thin Armor

Plate, A.^.G.

(a)- Tabulated and Interpolated from olot of about

100 reoultr..

Plate UriiU

G-13(w/o cover elate)

G-ll(no cover plate)

G-12(vrLth cover elate)

Grl0(w1th cover plate

Grll(v"ith cover plate

. Thlokna 8.P B.L.(f.o.)

5/16" •=440

7/16" ^478

7/16" «690 If* more than?701

9/16" more thanl769(oal.50)

-6-

Copnariaoh (b)

The oy.vct Jifferonce In foot-seoondfl in bftlllotio

limit aeterrainption between the definition of Gneo. 31

ar.i. AXS54 ifl very hftrd to ascertain. In some few ca.aea

no difference has been noted« In the great majority of

cacecs, horev r, there Lfl a, difference of from ''SO to

500 foot-seoonda In the result" obtainei. Averages of

the available re?ulta Bhon a difference (in favor of

3nec. "1) of ^OO f.s. for l/P" olate end of 400 f.s. for

1/4" plate« ^50 f.s. "'ill, therefore, b deducted

arbitrarily from the averages obtained of tests male

under Oioec. SI« Since there were r-.ome 000 nlates in this

grouo, both face-hardened and homogeneous, the actual

results and then the converted results '"ill be shown in

Table III.

■7-

All Re- BUltfl

8430 (^080)

»740 (»390)

^900 (^55^)

•^5^0 (PI50)

TA^L" Til

Surr.^n^-y oT Results of TtSts Under '.-neo. 31.*

(a) Plate Thioknero Ballistic Limite - f<ei

Mean Of Oomrerted to TTean of Converted All Recultü AXG54 Eculva-Hiahest to AXS54

lent. 10"/ of Eouivalent

5/1^" 1030 (1«30)

7/16« »JfO (^040)

I/o" pfi0Q (»9S0)

»/16«(o«l« »60) ^00 (1650)

* - From Partial RaoortS of Test Of Thin Armor

Plate, A.P.O.

(a) Tabulatei and Taken from Plot Involving about

900 repultai

Plate Equiv. Thicknesa p..L. if.o. )

GH» (w/o cover plate) 5/16« O440

Uli (w/o cover olate) 7/16" ?478

01° (with oov. r plate) 7/16" o500

3-10 (with cover plate) 1/?" more than »701

Gil (with cover plate) 9/16" more than 1769(cal. .50)

-8-

Comriarinon Je)

The plates used for groorlng wäre hOMogeneoua oiateo

of the OOlBDOSltion and heat treatment described at the

beginning of this rc-oort. Plates rubmltted under AXrj54

have oractically all been faos-hardened platen. However,

tventy-nine homogenc-ouG plates of this OOBDOSition and

heat treatment have been tented under Spec» AXo54. The

results obtained were afl follows:

1/4" Plates: - B.L.-l^lS, 1456, 1304, 1441, 1105,

1183, 1176, 1173, IP47, 1889«

Average 1864«: High 1456.

3/8" Plates: - B.L,-1738, 1811, 176?, 1844, 1755,

1877, 1854.

Average 1808: High 1877.

1/?" Plates: - B.L.-^m0, ^675, 8518, P431, 3P36,

8304, 8870, 8386, 8451, 8445.

Average 84C6 | High 8675.

3/4" Plate: - B.L.-1873

1" Plate: - B.L.-8445

The averages and highest valuer obtained were

plotted in Figure 4. From this olot the relative limit;:

of the grooved nlates under consideration may be eottparod«

The one value for the cal. .50 eouivalent Is very

oresumntive. The values for the other olates, however,

form a very fair basis for the conroarison shown in

Table IV.

• 0-

TABLE IV

Sumraffry of Resultfl of Ballictlc Testo

Homo^tneous .50C.-Cr-Mo-Va Armor Plates.-AXG54*

Plgte ThioknesG Ballistic Limit - f.G.^a^

Average Result Hlffoest Result

5/16" 1550 1630

7/16" 3180 p^65

1/P" 8400 ^675

9/16" (I470)(b^

* - From P.R. Tests of Thin Armor Plate, A.P.G-,

(a)- Interpolation from Fig. 1

(b)- Extrapolation - (very Questionable)

Plate Eouiv. Thickness B.L.(f.s.)

Gl?(w/o cover olate) 5/16" 3440

Gll(\-r/o cover plate) 7/16" ^78

Gl?(with cover plate) 7/16" 3590

0-10(with cover Plate) 1/3" more than 3701

ftlldrith cover plate) 9/16" more than 1769(cal. . 50 '

-10-

The results shown Ln Table IV are strictly com-

parntle. They run. obtained upon r)lates of the same

compositl »n and heat treatment and under the same firing

OOnditions« The increased ballistln limit for the came

weight of mat rial disposed as in these grooved plates

wan as follows:

Plate Exceeded Best B.L.

of same Wt of Identical Flat Plate by

n^(w/o sorer plate) 50fp

Hl(w/o cover Plate) 0 1/2$

3-18(with cover plate) 14 l/af

GrlO(wlth cover plate) more than if

Gil(with cover plate) more than 80M

*-roubtful - data Insufficient.

-11-

liaoiiBBion

Ia Then.' groove'! platen developed balllotic llmltu

from 18 to 36^ abovu those reouired in present

Bp0Oifioatlonfl (Table I ana summary following),

3. They vere from 9^ to 50^ more efficient than

the best of all plates on record of the same comnosltlon

and heat treatment. (Table IV)

3. Th:-y vere from 1^ to Iflf better th^n the average

of the best 10^ of all nlotes of all tynes tested at the

Proving O-round under the present specif ications. (Table II)

4. Although there may be differences of opinion

as to the exact difference between Spec. 31 and Spec.

AX354 insofar as their definitions of ballistic limit

are concerned, it is evident that the grooved plates

under consideration v/ero somewhat better than the best

lOf of all of the large number of nlp.tes tested under

Spec. 31. (Table III)

5. A plftte '"eighing that of l/?" flat plate

successfully withstood cal, .30 APT1 High Vel. ammunition.

This ammunition vas developed under an objective set by

the Chief of Staff to penetrate 1/3" armor at 300 yrd.

The results set forth in ".o.C.M. May 10th, 1934 show

how successfully that objective was met. It is, therefor.-,

of importance from the o^nosite point of view to have

obtained 0 test plate of 1/3" armor weight which

successfully withstood this ammunition as did plate G-10.

-13-

6, The value of the cover plate in this type of

armor Lfl not clerr. The cover plates used vere of the

name materif-'l M the grooved plate. Report ^llO/Z^

BhOWi th^t unleSi these cover plates were heat treated

to grr-pt hATdns^fl they did more harm then good. The

present result;:, do not make clear the advantage of the

crver plate. Two of the olates were enuivalent to 7/16"

armor in weight. The one With the cover nlate (G-l?) was

somewhat hatter thrn the one without a cover plate (G-ll).

G-10, which weighed the seme as 1/°" armor and which

Stopped the Tl ammunition, had a cover plate. On the

other hand, the greatest single increase in efficiency

was Shown by 013 v'ithout a cover nlate. In practice

these cover platen would be shot off the grooved olate

after a number of rounds and would have to be replaced.

Further investigation will be necessary before any

definite decision can be made regar-Unj the necessity

of cover plates in construction of this type. It is

felt that the only time the cover plate is of value is

when the bullet «rould otherwise strike directly at the

bottom of a groove. The area of groove bottoms (1/16"

on either fide of each groove) constitutes about lOf

of the surface area of the plate. Therefore, the cover

plate la useful to resist about 10^ of the rounds fired

at any plate and without it the plate should be Just as

effective against 90^ of the rounds fired against it.

-13-

7. A groove" Dlate of the tyoe BhOfm presents

no unusvftl . Ifficulty in rolllnn;. It "ould "be rolled

äov;n to a flat ilftt of desired thickness and then oaosed

between n<*lr8 of flat rolls and a grooved roll to the

desired size. The cost of nanufacture (except for the

initial cost of the grooved rolls) should not be any

greater than the cost for an eoual tonnage of flat

plates« No difficulties were experienced in heat treating

these grooved plates.

Conclusions

It is concluded that the method described herein

of disposing of a given veight of armor plate in a

plate grooved on the front and flat on the back has

resulted in a very definite increase in ballistic

efficiency.

Recommendations

It is recommended that this type of armor plate

be given further study in order that full advantage

may be taken of mechanical me^ns thus available for so

disposing of a given weight of material to obtain its

maximum usefulness.

Respectfully submitted,

?. yy Mar tin Isl/zt, Ord, Lept. U.G.Army

REPORT 710/42

GROOVED ARMOR PLATE

PLATE 610 FI6. 1

PLATE 6 II FI6.2

PLATE 612 FI6.3

QROQV&D ARMOR WLATC

PLATEL q 10

PLATE: qil

fiq. 2.

F»q. 3.

\

SK. 7lo/53.