By 1937, Japan fielded 1,060 tanks in 8 regiments, most designed for and used in the infantry-support role. But this focus left the IJA without a tank capable of taking on other tanks, a deficiency that was brought home hard during the battle of Khalkin-Gol, a decisive defeat inflicted by the Soviet Union on the Mongolian border in 1939. This proved fatal later when they faced the new generation of Allied tanks, as the great majority of the Japanese models were lightly armored, and not heavily gunned. As in the 1920s, with the priority of steel going to the navy and air force, the Japanese Army was relegated the remaining material for its tanks. Thus the 1930s-designed vehicles went on being mass-produced, and the warning of Khalkin-Gol was too slowly recognized. By 1940 they had the fifth-largest tank force in the world behind the Soviet Union, France, Britain and Germany, but were behind in medium and heavy tanks. However, after December 1941, with the entry of the United States into the conflict, priority continued to be given to warships and aircraft, weapons that were more conducive to naval warfare; attacking across the Pacific, and defending the Empire from the advancing Americans.