As the Russians began to make gains against the German army, both sides began to see the importance of the region of Kursk. After the harsh Russian winter, both sides had time to regroup during the spring. Russian factories churned out fresh supplies of war machinery, and Hitler unveiled his new plan, known as the Citadel. The July 5, 1943, meeting of the two opposing forces at Kursk became the biggest tank battle ever fought, utilizing six thousand tanks, four thousand aircraft, and two million soldiers.