The 4th Antiaircraft Artillery Battalion was commissioned on February 1, 1940, at Marine Corps Recruit Depot Parris Island, South Carolina.

[11] 4th Defense Battalion units at Pearl continued to man their positions until February 23, 1942, when they were relieved in order to prepare for movement to the South Pacific.

[12] The battalion provided air defense coverage for the island and endured a malaria epidemic during its first few months ashore.

In July 1942, the battalion provided a detachment, alongside Marine Aircraft Group 21 to protect the newly constructed airfield at Espiritu Santo helping to ensure the lines of communication between Hawaii and Australia remained open prior to the allied landings on Guadalcanal.

[13][12] In March 1943 the battalion departed Efate and sailed for New Zealand to rest and conduct additional training.

The 4th Defense Battalion came ashore on D-Day during the assault on Vella Lavella and established positions near Barakoma Airfield.

Between 15 August and 6 October 1943, the 4th Defense Battalion claimed to shootdown 42 Japanese aircraft during 121 total air raids.

During this time they were under the operational control of the Army's 81st Infantry Division as the area ground defense commander for Peleliu.