Commencing in May 1942, the brigade undertook occupation duties in Hanoi following the Japanese invasion of French Indochina, as part of the Southern Army. This was followed by a move to Malaya and then Rabaul at the end of the year, although the brigade's motor transport remained in Indochina. The 21st IMB arrived at Rabaul on 22 November; at this time it had not seen combat.