The T-34 was perhaps the most influential tank of World War II. Though there was no single revolutionary element in its design, it combined previous innovations into one strong and fast package. The model developed a fearsome reputation despite a bevy of practical problems. Initially, shoddy production quality caused many T-34s to break down in the field. Also early in the war Soviet tank doctrine was lackluster, commander and crew training were inadequate and tactical communication relied on primitive flag signals. Nevertheless, the T-34's ease of manufacture and all-around solid design made it crucial in rolling back German advances into Soviet territory. Its versatility also helped inspire the postwar concept of the jack-of-all-trades main battle tank.