As the Japanese advanced though Burma, they began air raids against Allied airfields and facilities in Assam from October 1942, and these progressed to South-East Bengal, Chittagong and Calcutta itself by December. 9 AA Brigade deployed batteries of 8 HAA guns at each of 15 airfields, as well as defending key supply points for the First Arakan offensive. 187 HAA Bty was detached with IV Corps.