| (iv) Introduction of Interlock Joints on Pz.Kw.IV In March 1942, when the Pz.Kw.IV was the heaviest vehicle in production (Tiger I was then about tocome into production), considerable discussion and correspondence arose over rebated joint manufacture and alternatives that could be used by adopting gas cutting to avoid the machining required on the former. The nose plate of the Pz.Kw.IV had then been thickened up to 80 mm. Extracts from suct correspondence betoween Rohland, head of the main commision for A.F.V. production and Oberat Rau of Wa Prüf 6 are given at appendices C and D. |
| That at Appendix C is an official report and comment, "testing of a B.W. Hull at Kummersdorf (proving ground) on 3rd March, '42". A lower hull structure of the B.W. vehicle (Pz.Kw.IV) had benn built by Krupp incorporating interlock joints between the gracis and nose and side plates instead of rebated, and a plug joint between nose and side plates. All these joints were made from gas cut plates. Further, therebated side to floor plate joint was changed to a simple overlap of the floor on the lower edge of the side plate. It is considered that the comments mad concerning the glacis plate being deflected downwards under attack from 3.7cm. and 5cm. A.P. shot and the consequent condemnation of the interlock joints to side plates overlooked that as the glacis plate was only 20mm. thick it would have deflected downwards similarly whatever tha joint to the side plates might be. method of construction with interlock joints was not introduced primarily for strength or ballistic resistance reasons. No comment need be made here concerning the production savings claimed as these are quite clearly given in Rohland's observations on gas cutting Appendix D (b). Attention is drawn, however, to the statements regarding the relief on the use of slotting and planing machine, and to the five proposals made by Rohland at the conclusion of his observations. It is quite apparent from these that there was no thought of turning to interlock construction on the Mk.IV in order to increase the strength of joints. It was solely to speed up and effect economy in the preparation of plates for welding by the use of gas cutting instead of machine tools. A word might be said with regard to the references to austenitic and ferritic electrodes in this correspondence. As Rohland stated, the use of these was independent of the question of gas cutting. The severe conditions of the Russian winter had caused much ferriteic tougher and more resistan to cold, austenitic electrodes, for the more commonly used ferritic. This matter is dealt with fully by Major Denaro, R.E. in his report on German Research and Development in Tank Armour Welding. The fact that the Army authorities confused the use of gas cutting with the austenitic v. ferritic electrodes issue, and that they did not think the production advantages worthwhile, or the re-training of welder warranted, (even though this letter was not necessary), is surely proof that the new method of construction with interlock joints was not introduced primarily for strength or ballistic resistance reasons. |
