The ROC Air Force was reconstituted into seven Groups, one separate Squadron and four Volunteer Groups. In 1939, after the USSR concluded a non-aggression pact with Germany, the Soviet Volunteer Group was withdrawn. By the end of 1941, the air force had 364 operational aircraft. Up to 100 of these were P-40Bs operated by the American Volunteer Group. U.S. replacement aircraft began to arrive in March 1942. They included A-29s, P-40s, P-43s,