15 cm sIG 33

The 15 cm sIG 33 (schweres Infanterie Geschütz 33, lit. "heavy infantry gun") was the standard German heavy infantry gun used in the Second World War. It was the largest weapon ever classified as an infantry gun by any nation.

Its weight made it difficult to use in the field, and the gun was increasingly adapted to various ad hoc mobile mountings. These were generically referred to as the SIG 33.

Development
Sources differ on the development history, but the gun itself was of conventional design. Early production models were horse-drawn, with wooden wheels. Later production models had pressed steel wheels, with solid rubber tires and air brakes for motor towing, albeit at a low speed (only carriages with pneumatic tires and suspension system could be towed at highway speeds). As with most German artillery carriages, the solid rubber tires and lack of springing meant that the gun could not safely be towed above 10 mph, and horse-drawing was still extensively employed.

The sIG 33 was rather heavy for its mission, and it was redesigned in the late 1930s to incorporate light alloys. This saved about 150 kg, but the outbreak of war forced the return to the original design before more than a few hundred were made, as the Luftwaffe had a higher priority for light alloys. A new carriage, made entirely of light alloys, was tested around 1939, but was not accepted for service.



Ammunition
Most of the shells used by the sIG 33 were unexceptional in design. The Stielgranate 42 was an exception. The finned projectile was mounted in front and outside of the barrel on a muzzle-loaded driving rod, and fired with a special propellant charge. The projectile had a range of about a 1000 m, with the rod separating at about 150 m. The Stielgranate 42 was designed for demolition and obstacle clearance, unlike the previous anti-tank Stielgranate 41.