puppet government of Manchukuo's army under the auspices of the Empire of Japan in the summer of 1940, and with it the Central Air Force Flight Academy that trained aviators for both civil and military. Equipped primarily with Nakajima Ki-27 fighters, the Manchukuo Imperial Army Air Arm were primary based in Fengtian (Shengyang) and Harbin. Towards the end of World War II, the Manchukuo Orchid Special Attack Force (kamikaze attack squadron) was established to counter the USAAF B-29 bomber raids on Manchukuo/NE territories. 1941 After withdrawing its volunteer pilots from China in the summer of 1940, the Soviet Union continued to supply aircraft to China until June 1941. Fighting continued on the northern front near Lanzhou, which was the Chinese terminus of the Chinese-Soviet transportation route. Chinese pilots were left to defend the northern front against Japanese air attacks. On 21 May 1941 eight I-15s of the 21st Squadron and one I-15 from the 29th Squadron flying in 2 formations on patrol encountered 27 Japanese bombers over Lanzhou. The first group of I-15s led by Squadron Commander Chen Sheng-hsing shot down one of the Japanese Mitsubishi G3M long range bombers and damaged another. On 22 May, 25 Japanese G3M bombers from the unit of Mihoro Kōkūtai were on a morning raid on Lanzhou. Seven Chinese I-16s of the 24th Pursuit Squadron and one Tupolev SB bomber of the 9th Bomb Squadron were ordered to disperse. Due to bad weather, the I-16s landed at Chung Chuan Chun Airfield just north of Lanzhou. As the Japanese bombers were sighted overhead, one of the I-16s flown by Kao You-hsing having just landed with the engine still running, took off to attack the Japanese planes, and shot down a G3M bomber flown by Lieutenant Shin-Taro Hashimoto and damaged another. The remaining six I-16s were able to take off and dispersed. On 26 May, Japanese fighters encountered 18 I-15s from the 29th Pursuit Squadron flying from Gansucheng to Lanzhou; two I-16s were shot down, both pilots bailing out, and the other 16 I-16s were destroyed on the ground when they landed for refuelling. Since World War II erupted in Europe on 1 September 1939 after Nazi Germany invaded Poland, the United States had maintained its neutrality until the unannounced Japanese air attack on the American naval base at Pearl Harbor on 7 December 1941. In October 1940, China appealed to American president Franklin D. Roosevelt