Historians of the Marine Corps have conducted significant research on the development of the Fleet Marine Force's amphibious assault mission. However, little has been written about the evolution of the defense battalion. From 1900 until 1940, advanced base defense's significance in Naval strategy surpassed or equaled amphibious assault. During 1940 and 1941, establishing defense battalions fell to the Corps' second priority. Likewise, few studies have examined Thomas Holcomb. As Commandant from 1936 through 1943, he installed the Corps as the premier seaborne support force and supervised its massive expansion. Commandant Thomas Holcomb was an excellent strategist, manager, and publicist. Understanding his actions will help illuminate the mentality and institutions of the military and government prior to World War II. The defense battalion provides a case study for examining Holcomb's leadership. Defense battalions also clearly found their roots in long standing advanced base defense theory. As Commandant from 1936 to 1943, Holcomb directed the Corps' expansion including the creation of the heavily armed defense battalion. On a tactical level, planners designed these units to defend island outposts against air, sea, and amphibious assaults Likewise, in holding island bases in the central and western Pacific, defense battalions fit into the grand strategy of the United States Navy. They comprised one half of the Corps' dual missions: amphibious assault and base defense. Finally, defense battalions served an equally pivotal public relations function Holcomb struggled to market the Marine Corps as a vital and unique branch of the American military. Serious challenges confronted Commandant Thomas Holcomb. For example, he was plagued by lack of funds, promotion stagnation, slow supply lines, and the isolationist tendencies of Congress and the American public. Throughout this study, the Corps' complete dependence on outside forces becomes abundantly clear. Sometimes Holcomb benefited from events beyond his control. Other times, he fought to turn seemingly damaging events into advantages for the Corps.