The United States Marine Corps (USMC) has a long history of seizing and defending advance bases;. Prior to World War I, base defense was the Marine Corps' main mission. l During World War I, the Advance Base Force was created to seize and defend enemy territory, primarily bases. In 1933, the Advance Base Force transformed into the Fleet Marine Force (FMF) under Commandant Major General Ben Fuller.2 By 1939, the looming threat of Japanese aggression in the Pacific solidified the need for' advance base defense and Commandant Major General Thomas Holcomb formed four Defense Battalions to defend advance naval bases from ground and air attack.3 The core of the original battalions were formed from two infantry battalions, 1st and 2nd Battalion, 15th Marine Regiment. 4 Subsequent Defense Battalions were formed with air defense personnel and artillerymen; infantrymen were attached as required. The first Defense Battalions included nearly 900 Marines, three anti-aircraft batteries, three seacoast batteries, and ground and anti-aircraft machine gun batteries.s Follow on evolutions included more sophisticated artillery, anti-aircraft guns and search radars. These Defense Battalions provided the first combined arms teams and proved to be very effective fighting forces.