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D.N.C. 5/JULY 1946.
Armour Technical Committee.
Meeting 15th August 1946.
Item 4. German Armour.
(a) Reports on visits to Germany.
With the fall of Germany opportunity has occurred for visits to the German Steel Works and for examination of German methods in armour manufacture to be investigated. There have been various reports circulated to the Committee of this visits of Mr. D.E.J. Offord of D.N.C. and Mr. Walker of Messrs. Firth-Brown Ltd., to Czechoslovakia and germany, and those of Lieut. Commander B.R. Queneau U.S.N. to Dortmund and Essen. In regard to ship armour the reports stress the importance attached by Krupp, Essen, to low sulphur and phosphorus steel for armour manufacture. The Baoic (Basic (sic!)) Open Hearth furnace appears to be the main source of steel supply and elaborate precautions are taken to ensure deoxidation and desulphurization of the steel. The employment of a chromo recovery process for the manufature of armour at Krupp, Essen, is mentioned by Lieut. Commander Queneau U.S.N. in his report, it is believed that this process only applies in the production of low alloy steels for Tank armour and not normally for ship armour. The analysia employed by the Germans for heavy ship armour is similar to our own. In regard to manufacture of the finished armour plate it would appear that the German practice is to roll direct from slab ingot without forging, to avoid as they say, lamination in the finished plate. Treatment of the armour does not differ markedly from that employed in this country. For cemented armour the German prefers a deep face and produces this by carburising for a longer time than we do, thereby ensuring deeper carbon penetration. The process produces higher percentages on the plate face which would seem to be undesirable in the light of our own experience.
It is suggested that the Committee might consider in the light of additional evidence which may be available, wether there are any factors in the fundamentals of steel making, brough to light by the German visits which are worthy of investigation for British armour manufacture.
(b) Armour on Tirpitz
Armour plating removed from the ex German Battleship TIRPITZ was shipped to this country in August 1945, and arrangements were made for full metallurgical and physical examinations to be made by each of the three armour firms. Separate portions of armour (a) uniform thickness 12 1/2 " (b) tapered thickness 12 1/2 " - 6 1/2 ", from side armour of the vessel, and (c) cast armour believed from control tower or range finder hood were examined and reports have been received from the three firms as follows: -
A summary of the analysis of plates and mechanical properties of the German armour is given on the attached sheet which includes for comparison plates of British manufacture. The main point of interest on this sheet is the low sulphur and phosphorus and the greater reduction of area obtaining on the German armour.
The most important point brought to light by the investigation was the greta depth of hard face on the German armour. To the 300 Brinell level the German plates have approximately 45 - 50 per cent depth of face. In British plates 25 per cent - 35 per cent is the more usual practice.
The castings examined were of a low carbon analysis as [continued on next page]
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follows, .15 per cent C., 3 per cent Cr., 0.3 per cent Mo., 0.1 per cent Va, having a maximum stress of 40 -42 ton/in2 and Ized 80 - 100 ft. lbs.
They were free of unsoundness.
Firing trials against a number of the armour plates from TIRPITZ have taken place at Shoeburyness.
The 12 172 " plates were attacked by 15" A.P.C. Shell at 30° angle firmpact, in two groups.
(b) Large plate No.27885 roughly 11' x 9'-6" for penetration and perforation limits
A summary of the results obtained for Groups (a) and (b)is as follows:-
(a) Small plates approximate size 4'-6" x 5'-6".
Velocity. Result - Shell Plate damage.
1539 fs. Perforation - whole Broke into pieces.
1507 fs. Stop - broke up on plate. Broke into two pieces.
1501 fs. Penetration - frags. front&rear. Holed. Broke into three pieces.
1456 fs. Stop - broke up on plate. Smooth bulge.
1450 fs. Stop - broke up on plate. "
1348 fs. Stop - broke up on plate. "
From plate No.27885.
1508 fs. Peforation - whole. Broke into three pieces and disced.
(b) Plate No. 27885. Size 11" x 9'-6" .
Velocity. Corrected velocity Result - Shell . Plate damage.
1497 fs. 1507 Perforation - whole Disced and broke away to top edge.
1454 fs. 1462 Penetration. Frags. front and rear. Hole 13" x 11.8"
1371 fs. 1379 Stop - Broke up on plate. Smooth bulge 12" x 14"
D.N.C. was mainly interested in the performance of the large plate No.27885 and it would appear from the results obtained that
Limit of perforation = 1485 fs. ± 23 fs.
Limit of penetration = 1420 fs. ± 42 fs.
For comparison with these results we had the figures for two British 520 lbs. C, plates used for proof of supplies
Firth-Brown Ltd., No.5020 3 1/2" Face 1389 fs. (Penetration).
E.S.C. No.9894 3 1/4" Face 1377 fs. ± 17 fs. (Penetration).
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In regard to penetration limit, therefore, there was an apparant superiority in favour of the German armour of the order of 30 - 40 fs. This may have been an under estimate of the difference since in assessing the penetration limit of the German plate the possible error was as much as ± 42 fs.
It was interesting to examine the results of trials against E.S.C. 9894 in relation to those obtained on the German plate in order to determine if possible the the order of difference with more accuracy.
E.S.C. 9894 1373 fs. 1394 fs. Damage Hole 9.2" x 10.8" Plug/disc 19" x 14" Lip 1.5"
TIRPITZ. 27885 1454 fs. 1462 fs. Damage Hole 13" x 11.8" Plug/disc 22" x 13" Lip 2".
i.c. the damage were comparable for a velocity difference of 68 fs. in favour of the German plate.
Whilst it was not a strictly fair, on the above basis of comparison, to assume that, in regard to penetration limit, the same difference would apply it seemed reasonable to state that the German Plate No.27885 showed a superiority over the British armour of the same thickness of about 50 fs under attack by 15" A.P.C. Mark XVIIB shell at 30°.
Little information was available regarding perforation limit of British armour. Trials have been undertaken against E.S.C. No.9894 to establish the limit of perforation. The following results were obtained.
E.S.C. 9894. Damage.
Velocity Corrected Velocity Shell. Front. Back.
1. 1439 fs. 1463 fs. B.U.O.P. Stop Smooth bulge.
2. 1504 fs. 1528 fs. B.U.O.P. All frags. in front. Hole 12.5"x14" Disc 42" x 42".
3. 1555 fs. 1582 fs. Perforation (broken). Hole 20.8"x31.2" Disc 72" x 50".
Note in round 3 shell was recovered just behind the plate.
The assessed limit of perforation of this E.S.C plate was 1582 fs. (shell broken) on the above results.
The assessed limit of penetration of the German plate 27885 was 1485 fs ± 23 fs. (shell whole).
The remarkable feature of this trial is that the deep face on the German plate did not break-up the shell at perforation velocity. The lesser face of the British plate did so and gave a result approximately 100 fs higher for perforation.
The result on E.S.C. 9894 where a stop was obtained at a velocity of 1463 fs (corrected for thickness), is at variance with Proof of Supply result where the limit was assessed as 1377 fs. This is due to the fact that, at the trial for proof of supplies on 30th June 1943, the first round at bottom of ingot plugged the plate at a velocity of approx. 1400 fs (corrected for thickness). The general quality of the plate is felt is more keeping with a limit assessed on the second trial namely 1485 fs ± 35 fs (corrected for thickness).
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In conclusion it seems that if Plate No.27885 and No.9894 are generally representative of German and Britsih armour then,
(a) Penetration Limit.
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COMPARISON OF BRITISH & GERMAN (EX TIRPITZ) CEMENTED ARMOUR.
ANALYSIS 520 LBS THICKNESS.