 Complete the following phrase:  In August 1937, the Chinese Kuomintang Government signed a non-aggression pact with the USSR. And, in autumn of the same year, the Soviet Union commenced to ship I-15s as a part of a programme of military aid to the Chinese Air Force CAF in its defensive war against Japan. More than 250 Soviet pilots volunteered to fly the 255 I-15s supplied to China in autumn 1937. By 1939, the total number of Polikarpov biplanes delivered to CAF reached 347 I-15I-15bis. The I-15bis saw a great amount of action in the SovietJapanese border conflicts along the ChinaMongolia border. From 1938-1941, I-15s in the Nationalist Air Force of China, fought many major battles, and skirmishes against invading and occupying Japanese forces, including the Battle of Taierzhuang, the Battle of Wuhan, the Battle of South Guangxi, the 