The Curtiss Model 68 Hawk III biplane, built both in the US and China, was used by the ROCAF as a bomber as well as the primary fighter during the early part of the war. It took the brunt of the Japanese attack during the defense of Shanghai and Nanjing, helping to make flying aces of several Chinese pilots. Shortly after the conflict began, a Chinese Air Force fighter pilot intercepted a land-based Japanese bomber group from Taiwan and shot down a Mitsubishi G3M medium bomber. This was the first aerial combat victory for the Chinese. In addition to Curtiss Hawk IIIs, the ROCAF opposed Japanese attacks with some older Curtis Hawk II, Boeing P-26 “Peashooter”, Gloster Gladiator, and Fiat CR.32 fighters. After attrition had taken its toll of these aircraft, they were replaced by Soviet Polikarpov I-15 biplane fighters and later by Polikarpov I-16 aircraft, the world's first low-wing monoplane fighter with retractable landing gear used in combat. The latter also had 20mm cannons, making it one of the most heavily armed fighters for the period.