in 1941, following japan's entrance into the war, the battalion was mobilised for war and placed on full-time duty with the task of defending the area between port douglas and gordonvale. later they were sent to townsville, where they experienced japanese air raids, before being sent to cairns as preparations were made to deploy the battalion overseas. in 1943, however, a manpower shortage had developed within the australian economy as a result of an overmobilisation of the military. subsequently, the government released a large number of rural workers from their full-time military commitment and decided to disband or amalgamate a number of militia units. as a result, the 51st battalion was forced to amalgamate with the 31st battalion, kennedy regiment on 12 april 1943.