Guangxi. At the beginning of 1940 it moved to Yunnan for defense of the Kunming-Mengzi railroad, which was subjected to massive air attacks. At the end of May the squadron returned to Chonqing; it did not have enough serviceable Hawk 75s, and was supplemented with nine old Hawk III biplanes from the 22nd Squadron. 1940 On 8 February 1940, 27 Japanese planes heading for Mengzi were intercepted at 3.05 pm by three Hawk 75s of the 18th Squadron taking off from Kunming. In the ensuing dogfight, one Hawk 75 (No. 5024) was damaged and forced to crash land; its pilot Yang Tzu-fan was injured. On 13 February 1940 three Hawk 75s of the 18th Squadron intercepted 27 Japanese bombers which were on their way to bomb the bridge near Siulungtam. The Hawk 75s hit one Japanese bomber and were later joined by three I-15 biplane fighters. Together they made many passes at the damaged bomber, killing the upper gunner. The Chinese claimed to have finally shot down the hapless plane. Several of the Chinese planes were slightly damaged and one pilot, Tseng Pei-fu, was injured. While the Mitsubishi A5M was the most-advanced fighter in the Chinese theatre since September 1937, the Japanese were soon to introduce the world's most advanced fighter aircraft into China in the summer of 1940; the Mitsubishi A6M "Zero". The new Zero was far superior to the A5M predecessor, the Soviet I-16 and American Hawk 75 fighter planes. The Chinese Air Force issued a general directive to its air units to adopt an "air dispersal tactics", and to avoid direct confrontation with Japanese fighters whenever possible. On 4 October 1940 six Hawk 75s of the 18th Squadron were following the order to disperse to Guanxian when 27 Japanese Mitsubishi G3M bombers escorted by eight Japanese A6M Zeros led by Lieutenant Tamotsu Yokoyama on a bombing raid to Chengdu. The Japanese Zeros caught up with the Hawk 75s and shot one down, wounding the pilots of another two and forcing them to crash land, and set two Hawk 75s on fire on the ground while refueling. By December 1940 the 18th Squadron had ceased to exist in reality, and was disbanded in January 1941. The Hawk 75 fighters in the Chinese Air Force were later replaced by the American Curtiss P-40. The Manchukuo Imperial Army Air Arm The Manchukuo Imperial Army Air Arm was established for the