Dart Shaped Shell
(6) Fin Stabilized
21 cm Rochling Shell, Inert






















picture: D. Nagott

The Rochling Shell was developed for attacks of concrete and armor plate but has only proved effective against the former.
 Essentially the projectile is a very long S.A.P. shell intended to pierce the walls of an emplacement and explode in the rear.
 The body is made from one forging with a solid nose. The front tip is hardened throughout but towards the rear of the solid head only the outer layers are hardened leaving the material at the centre relatively soft. A manganese silicon steel was said to be used, the maximum tensile strength of the fully hardened parts being 160-180 kg/mm2 while the rest of the body was about 105-120 kg/mm2.
The shell body diameter is 127 mm and the length about 2300 mm. An internal cavity of maximum diameter of about 75 mm contains some 8 kg of F.P. 10, (T,N.T. with 10% Montan wax). Fuzed with the Bd Z 5141.
A small SO3 spotting charge at the nose is functioned superquick for spotting.
 Tangentially folding fins are fitted to the rear of the projectile and a metal case slid over the rear.
There is a cavity in the rear of the case and a 3 mm diameter hole in this cavity allows the propellant gases to build up a pressure in the cavity of the order of 500 atmospheres with a maximum gun pressure of 1500 atmospheres.
 After shot ejection, this internal pressure is used to expel the rear case backwards, and the fins then expand. This system of expelling an unwanted rear attachment was first applied to the Rochling shell but was later universal on all German projectiles and in particular is exploited on the P.P.G.
 The shell body is multi-grooved at the shoulder to take a multi-perforated sabot, released by plungers setting back. The body is also slotted to contain a segmented ring over which the lip of the rear case fits. A further multi-perforated sabot ring fits over the front of the case, and a lip of the sabot of low diameter abuts against the segmented ring in the body slot so that the rear sabot ring constitutes a tie preventing the projectile body slipping forward relative to the case on loading.
 A driving ring, perforated at it's centre to allow propellant gases to enter the cavity is screwed on the rear. This is fitted with a sintered iron driving band
 A graphited paper gasket between the driving ring and the projectile body allows relative slip to take place so that the full rotation is not transferred to the projectile.
 There were round to round variations in the amount of spin actually possessed by each shell fired, but this was said not to effect the accuracy of the projectile which was stated to have a 50% zone of 0,7% of the range.
The most accurate models were said to possess six fins. In certain circumstances the rear case, witch was rapidly shot off, might injure personnel manning the gun.
 Final development trials in the 21 cm Morser 18 an M.V. of 550 m/s was attained for a projectile weight of 193 kg compared with 370 m/s for the 113 kg standard shell. Comparative lengths of penetration into the best Czech concrete were stated to be 220 and 115 cm at muzzle velocity. Other reports stated 220 and 360 cm against concrete and 50 m into earth.
 The performance of the long projectile was not excessively degraded at high angle attack but it was of no use against armour plate. An experiment carried out on the Western Front against underground storage chambers was mentioned in which the projectile penetrated a great depth of earth and the concrete roof, exploding inside the chamber.
 A full-bore Rochling shell for 37 mm and 50 mm guns was developed along with a 15 cm model in 1939 for the attack of armour plate, but was not put in the German service. Work began on the 21 cm weapon in 1940 but had been held up. The first experimental service projectiles had been made in 1944, but the course of events had not permitted their use. Further projectiles of the same type were under development in the French 34 cm railway gun and the 35 cm Morser, M1.