Röchling shell

Röchling shells were bunker-busting artillery shells, developed by German engineer August Cönders during World War II, based on the theory of increasing sectional density to improve penetration.

Röchling shells were tested in 1942 and 1943 against the Belgian Fort d'Aubin-Neufchâteau

The shells were able to penetrate more than 4 m of reinforced concrete, but had low muzzle velocity, and as such were very inaccurate: 36 m on 1000 m range. As a result, they saw very limited use during World War II; only about 200 shells were ever fired.

Röchling shells were developed for the 21 cm Mörser 18, 34 cm railway gun 674(f) and for the 35.5 cm Haubitze M1 only.

They were regarded as a secret German weapon, and there is speculation that the limited use was in order to reduce the chance of dud shells being captured and exploited by the Allied forces. A more likely reason, however, is the poor accuracy of the shells.