The participation by Soviet 'volunteer' tank units in the Spanish Civil War was decisive in forming Soviet tank designs for World War II. Soviet tanks dominated their foreign rivals in Spain due to their firepower, but their thin armor, in common with most tanks of the period, made them vulnerable to the new towed antitank guns being supplied to Infantry units. This finding led directly to a new generation of Soviet tanks. By the eve of World War II, the Soviet Union had some of the world's best tanks (including the T-34 and KV-1, which were basically a generation ahead, coming as a shock to the Wehrmacht). However, the poor training and readiness status of most Red Army units led to a catastrophic defeat of the enormous Soviet Mechanised Corps during the opening phases of Operation Barbarossa, Germany's 1941 invasion of the Soviet Union. Despite their generally good equipment, the Red Army's operational capabilities and motorised logistic support were very inferior.