Organization and Equipment for the Defense Battalion

Envisioned as combined arms teams capable of delivering intense firepower, defense battalions were expected to have their greatest impact in the kind of campaign outlined in the Orange plan. The Navy's seagoing transports provided strategic mobility for the defense battalions, but once ashore, the units lacked vehicles and manpower for tactical mobility. Because the battalion became essentially immobile when it landed, each member had a battle station, as on a ship, to operate a particular crew-served weapon or other piece of equipment. As configured in 1939 and 1940, a defense battalion could achieve mobility on land only by leaving its artillery, searchlights, and detection gear and fighting as infantry.

Marine Corps defense battalions could operate as integral units in support of a base or beachhead, positioning their weapons and equipment to cover assigned sectors and meet specific threats. Moreover, they might form detachments with a size and armament suitable for a particular task, such as defending various islets within an atoll or protecting separate beachheads. Although relatively static when in place, the ability of the battalions to divide in this fashion provided a kind of flexibility that may not have been fully appreciated in 1939, when the basic concept placed one battalion, though of variable size, at a given place.

MajGen Charles D. Barrett, while a colonel, together with LtCol Robert H. Pepper, played a major role in the development of the defense battalion. Department of Defense photo (USMC) 61403

Because a defense battalion could, in effect, form task organizations, it somewhat resembled the larger infantry regiment, which could employ battalion combat teams. According to Lieutenant Heinl, in terms of "strength and variety of material," the defense battalion "might well be a regiment. Actually, the seacoast and antiaircraft artillery groups are almost small battalions, while the other three separate batteries (search light and sound locator and the two machine gun units) are undeniable batteries in the accepted sense of the word."

Despite the lieutenant's enthusiasm for the defense battalions, they had definite weaknesses, particularly in infantry and armor for mobile reserves in the event of a large-scale enemy landing. The failings, however, seemed acceptable to the General Board of the Navy — roughly comparable to the War Department's General Staff — which felt that the battalions could nevertheless protect outlying bases against raids by aircraft, ships, and comparatively small landing parties. Concern that the defense battalions, in their current configuration, might not be able to repulse more ambitious hostile landings caused the Marine Corps to debate, during the spring of 1941, the feasibility of creating separate infantry battalions to fight alongside the defense units.

The proposed 850-man infantry battalions would forestall any possible need to detail infantrymen from the regiments to reinforce the defense battalions. Consequently, Secretary of the Navy Frank Knox approved the creation of separate infantry battalions to serve with the defense battalions. After the Japanese attack on Pearl Harbor, the regiments and divisions — and for a time the specialized units such as the raiders — demanded a lion's share of manpower, and with few exceptions, the defense battalions had to fend for themselves without the planned infantry battalions, though occasionally with an organic rifle company. Every Marine in a typical defense battalion had to train to fight as an infantryman in an emergency, with the members of gun and searchlight crews leaving their usual battle stations. Rifle companies served at various times with the 6th, 7th, and 51st Defense Battalions, and such a component was planned for the 52d, but not assigned. Those battalions that included a company of infantry bore the title "composite."

Improvements in equipment, a changing strategic situation, and deployment in areas that varied from desolate coral atolls to dense jungle ensured that no single table of equipment or organization could apply at all times to every defense battalion. Each of the organizations tended to be unique — "one of a kind," as a battalion's history stated. Weapons and personnel reflected a unit's destination and duties, much as a child's erector set took the shape dictated by the person assembling the parts, or such was the view of James H. Powers, a veteran of the 8th Defense Battalion. The selection and assignment of men and equipment proved a dynamic process, as units moved about, split into detachments, underwent redesignation, and traded old equipment for new. Much of the weapons and material came from the stocks of the U.S. Army, which had similarly equipped coast and antiaircraft artillery units. The first 155mm guns dated from World War I, but the Army quickly made modern types available, along with new 90mm antiaircraft guns that replaced the 3-inch weapons initially used by the defense battalions. In addition, the Army provided both primitive sound-ranging equipment and three types of Signal Corps radar — the early-model SCR268 and SCR270 and the more advanced SCR268, which provided automatic target tracking and gun-laying.

By October 1941, the tables of organization for the new defense battalions had certain features in common, each calling for a headquarters battery, a sound-locator and searchlight battery, a 5-inch seacoast artillery group, a 3-inch antiaircraft group, and a machine-gun group. The specific allocation of personnel and equipment within each battalion depended, however, on where the battalion deployed and the changes "prescribed by the Commandant from time to time." In brief, the defense battalions adhered to certain standard configurations, with individual variations due to time and circumstance. The average battalion strength during the war was 1,372 officers and men, including Navy medical personnel. Like manpower, the equipment used by the defense battalions also varied, although the armament of the typical wartime unit consisted of eight 155mm guns, twelve 90mm guns, nineteen 40mm guns, twenty-eight 20mm guns, and thirty-five .50-caliber heavy machine guns, supplemented in some instances by eight M3 light tanks.