ZSU-23-4 “Shilka” (2A6) The previous Soviet self-propelled anti-aircraft gun (SPAAG), the ZSU-57-2, was armed with two 57 mm autocannons; it was aimed optically using a basic tracking and lead calculating system. The ZSU-57-2 was not particularly successful despite its very powerful autocannons; given their large caliber, it could only carry 300 rounds, was inaccurate as it ...