The Manchukuo Imperial Army was the ground component of the Empire of Manchukuo's armed forces and consisted of as many as 170,000 to 220,000 troops at its peak in 1945 by some estimates, having formally been established by the Army and Navy Act of 15 April 1932. The force included members of all the major ethnic groups of Manchukuo, which were trained and led by Japanese instructors and advisors. Despite the numerous attempts by the Japanese to improve the combat capability of the Imperial Army and instill a Manchukuoan patriotic spirit among its troops, the majority of its units were regarded as unreliable by Japanese officers. Their main role was to fight Nationalist and Communist insurgents that continued to resist the Japanese occupation of northeastern China, and occasionally the Manchukuo Imperial Army took part in operations against the Chinese National Revolutionary Army and the Soviet Red Army (usually in support of the Imperial Japanese Army). Initially its members were former soldiers of Marshal Zhang Xueliang's warlord army who had surrendered to Japan during the Japanese invasion of Manchuria. But since the Young Marshal's former troops were largely not loyal to the new regime and performed poorly against partisans, the new government of Manchukuo took efforts to recruit—and later draft—new soldiers. In 1934 a law was passed stating that only those that had been trained by the government of Manchukuo could serve as officers. The Military Supplies Requisition Law of 13 May 1937 allowed Japanese and Manchukuo authorities to draft forced laborers. The actual calling up of conscripts for the army did not begin until 1940, at which point all youths received a physical and 10% were to be selected for service. Between 1938 and 1940, several military academies were established to provide a new officer corps for the Imperial Army, including a specific school for ethnic Mongols.