Early Mobilization
Marine Corps strength increased accordingly. President Roosevelt had authorized an increase to 25,000 enlisted men in 1939, and in the fall of 1940 he approved the recall of Marine Corps retirees and the mobilization of Reservists, which added another 15,000 men to the Corps.
Global Crisis
The national emergency was upgraded to "unlimited" status in May 1941, in response to the worsening global crisis. In mid-1941 the maximum figure for Marine Corps total strength was bumped to 50,000 officers and enlisted. The Navy and Marine Corps soon realized this would be insufficient if the fleet were to prepare for an Atlantic and Pacific war; they requested authorization to expand the Marine Corps to over 150,000. Congress assented and by December 1941 over 65,000 men wore a Marine Corps uniform.
Escalation of War
As war escalated in Europe during 1940, the U.S. awakened to the possibility of German attacks against American possessions in the Atlantic and Caribbean, and, worse, an attack against the U.S. itself. As a result, in early 1941 the Fleet Marine Forces (FMF) was reorganized, expanding the 1st and 2nd Marine Brigades into the 1st and 2nd Marine Divisions (MarDiv), to be quartered on the East and West coasts, respectively; the 1st and 2nd Marine Air Wings (MAW) and the defense battalions rounded out the FMF.
Increased Mobilization
The German threat, increasing mobilization, and the space limitations at Parris Island, South Carolina and Quantico, Virginia all underscored the need for one large East Coast Marine base that could serve as a training center for approximately 15,000 men. Furthermore, at that time the Army-Navy Joint Board (predecessor of the Joint Chiefs of Staff) still assumed that joint Marine Corps and Army amphibious forces would be needed if the U.S. were called upon to liberate its European allies. The Corps would need an operational staging area of its own, but Parris Island and Quantico were already overcrowded and too small to serve this purpose. The need for a new Marine base was critical, and haste was required.