In the summer of 1943, elements of the 9th, 10th, and 11th Defense Battalions supported the Army's XIV Corps in the central Solomons campaign. In 1944 additional battalions helped clear the northern islands, including Bougainville. By the end of 1943, the Defense Battalions reached a maximum strength 26,685 Marines across 19 Battalions. As the threat to advanced naval bases decreased later in the war, Defense Battalions were decommissioned or reformed as anti-aircraft battalions.