 The 3rd, 12th, 60th and 98th Air Groups, based in French Indochina, struck British and Australian targets in Thailand and Malaya, bombing Alor Star, Sungai Petani and Butterworth under escort by Nakajima Ki-27 and Ki-43 fighters.However, starting from operations over Burma in December 1941 and early 1942, the Ki-21 began to suffer heavy casualties from Curtiss P-40s and Hawker Hurricanes.To partially compensate, the IJAAF introduced the Ki-21-IIb, with a pedal-operated upper turret with one 12.7 mm (0.50 in) Type 1 machine gun, redesigned cockpit canopies and increased fuel capacity.