During World War II (1939-1945), the Soviet armored doctrine underwent significant revision in response to the German invasion known as "Operation Barbarossa." One notable shift was towards emphasizing mobile artillery support, including the use of rocket fire systems such as the "Katyusha," along with towed artillery and Self-Propelled Gun (SPG) units. This wartime experience greatly influenced post-war designs, with vehicles featuring large-caliber guns becoming standard for supporting major offensives.