The Battle of Kursk was the largest tank battle in history, involving some 6,000 tanks and 2 million troops. Following their defeat at Stalingrad, the Germans launched Operation Citadel to pinch off a Soviet salient at Kursk. However, the Soviets had received intelligence about the plan and built massive defensive lines, including minefields and anti-tank ditches. The battle featured the debut of the heavy German Tiger and Panther tanks, but the sheer number of Soviet T-34s and the depth of their defenses proved insurmountable. After the failure of the offensive, the strategic initiative passed permanently to the Soviet Union. From this point on, the Red Army remained on the offensive for the rest of the war, eventually reaching the gates of Berlin.