US Marine Corps Pacific Theater of Operations 1941–43

Pooposals fior Marine divisions date back to World War 1, but through the years the most practical size for Marine expeditionary forces was the brigade, usually consisting of two small regiments. In September 1940 the Navy Department directed that table of organization (T/0) be developed for a Marine division.
While the leaglity of the Navy Department raising divisions was studied, the Navy sought no advice from the Army on the organsization of divisions, their logisitcal requirements, or internal command and control. On February 1, 1941 the 1st and 2d MarBdes, FMF were redesignated the 1st and 2d MarDivs respectively, under B-100 T/O.