Shortly after the United States entered World War II, the Allies agreed that the European Theater would have priority in the war over the Pacific Theater. The Marine Corps' war was in the Pacific and all war plans regarding the employment of Marines reflected that. Nevertheless, because the Marine Corps was part of the naval establishment, it had responsibility also for furnishing men to parts of the Navy assigned to the European and Mediterranean theaters and to the operations conducted there.
Read also21st Century U.S. Military Manuals: Sniper Training - FM 23-10 - Marksmanship, Equipment, Ballistics, Weapon Capabilities, Sniping Techniques (Value-Added Professional Format Series)
Professionally converted for accurate flowing-text e-book format reproduction, the Sniper Training Army field manual (FM 23-10) provides information needed to train and equip snipers and to aid them in their missions and operations. It is intended for use by commanders, staffs, trainers, snipers, and soldiers at training posts, Army schools, and…
These were not large Marine formations, but were, for the most part, individual Marines and small detachments assigned to guard duty at the barracks and naval operating bases established in the United Kingdom, or men assigned as "sea-going" Marines in the detachments of the large fighting ships. Another category was filled by those intrepid Marines who volunteered for duty with the Office of Strategic Services (OSS), to undertake covert operations with the underground against the Nazis in the occupied countries of Europe and North Africa.
In April 1941, Congress stipulated that Marine Corps strength should be 20 percent of that of the Navy. Only a relatively few Marines were detailed to the Atlantic, and they were primarily assigned to the Navy to perform their traditional functions, that of security of naval installations and service afloat. Though few in number, they made a significant contribution, though largely overshadowed by the exploits of their fellow Marines in the Pacific.
The U.S. Atlantic Fleet in 1941 comprised four old battleships, New York (BB 34), Texas (BB 35), Arkansas (BB 33), and Wyoming (BB 32); one division of heavy cruisers, San Francisco (CA 38), Tuscaloosa (CA 37), Quincy (CA 39), and Vincennes (CA 44); the aircraft carrier Ranger (CV 4); and a destroyer squadron. The carrier Wasp (CV 7) would join the fleet shortly upon its commissioning. Marine detachments were assigned to these ships.
Marines have traditionally served as part of the complement of naval warships. In World War II, this service was confined mostly to the larger-sized ships —battleships (BB); cruisers, both heavy (CA) and light (CL); and carriers and light carriers (CV or CVL). Smaller ships normally carried a Marine detachment only when they served as flagships.