Following the entry of Japan into the war in December 1941, and their subsequent advance through Malaya and New Guinea, units of the Militia were called upon to carry out garrison and defensive duties around Australia in response to the perceived threat of invasion. The 2nd Brigade was mobilised at Mount Martha, and initially assigned to defend the Melbourne area. In this role, two battalions were deployed to Flinders and Portsea, while brigade headquarters and two other battalions remained around Red Hill. Following this the 14th and 32nd Battalions were merged and later transferred to the 6th Brigade. In February 1942 the Melbourne University Rifles were also removed from the brigade's order of battle.