 Complete the following phrase:  The USSR volunteer squadrons often flew their missions together with Chinese squadrons. From the beginning of 1938 to May 1940, USSR squadrons participated in more than 50 major air battles and together with Chinese squadrons shot down 81 Japanese aircraft, damaged 114 and 14 Japanese warships. In the summer of 1940, the USSR withdrew their volunteer pilots, leaving only a small number of advisers and technical personnel in China. They continued to supply aircraft to China until June 1941 when Germany 