1st Marine Division

The 1st Marine Division (1st MARDIV) is a Marine division of the United States Marine Corps headquartered at Marine Corps Base Camp Pendleton, California. It is the ground combat element of the I Marine Expeditionary Force (I MEF).

It is the oldest and largest active duty division in the United States Marine Corps, representing a combat-ready force of 22,000 personnel. It is one of three active duty divisions in the Marine Corps today and is a multi-role, expeditionary ground combat force. It is nicknamed "The Old Breed".

The division is employed as the ground combat element (GCE) of the I Marine Expeditionary Force or may provide task-organized forces for assault operations and such operations as may be directed. The 1st Marine Division must be able to provide the ground amphibious forcible entry capability to the naval expeditionary force (NEF) and to conduct subsequent land operations in any operational environment.

As of January 2025 1st Marine Division currently comprises a headquarters battalion, four regiments and five separate battalions as follows:

The lineal forebear of the 1st Marine Division is the 1st Advance Base Brigade, which was activated on 23 December 1913 at Philadelphia, Pennsylvania. (Subsequently, the brigade was redesignated on 1 April 1914, as the 1st Brigade, and on 16 September 1935, as the 1st Marine Brigade). The brigade consisted of the Fixed Defense Regiment and the Mobile Defense Regiment, later designated as the 1st and 2nd Regiments, 1st Brigade, respectively. In 1916, while deployed in Haiti, the two regiments were again redesignated, exchanging numerals, to then become the 2nd and 1st Regiments, 1st Brigade. Between April 1914 and August 1934, elements of the 1st Brigade participated in operations in Mexico, Haiti, the Dominican Republic, and Cuba, receiving campaign credit for service in each nation. While the 1st Brigade did not serve ashore in the European theater during the First World War, the brigade was awarded the World War I Victory Medal Streamer, with one bronze star, in recognition of the brigade's service during that conflict. On 16 September 1935, the brigade was redesignated as the 1st Marine Brigade and deployed to Guantanamo Bay, Cuba in October 1940.

The 1st Marine Division was activated aboard the USS Texas on 1 February 1941. In May 1941, the 1st MARDIV relocated to Quantico, Virginia and Parris Island, South Carolina and in April 1942, the division began deploying to Samoa and Wellington, New Zealand. The division's units were scattered over the Pacific with the support elements and the 1st Marine Regiment transported en route to New Zealand on three ships, the USATs Ericsson, Barnett and Elliott from Naval Reserve Air Base Oakland to New Zealand, and later were landed on the island of Guadalcanal, part of the Solomon Islands, on 7 August 1942.

Initially, only the 7th Marine Regiment was in garrison on British Samoa, with the 5th Marine Regiment having just encamped at Wellington, New Zealand after disembarking from USAT Wakefield, and the 1st Marine Regiment not scheduled to arrive in New Zealand until 11 July. The 1st Raider Battalion was on New Caledonia, and the 3rd Defense Battalion was in Pearl Harbor. All of the division's units, with the 11th Marines (artillery) and 75mm howitzer armed 10th Marines battalion would rendezvous at Fiji.

Due to the change in orders and shortage of attack and combat cargo vessels, all of the division's 2.5-ton trucks, M1918 155-mm howitzers and the sound and flash-ranging equipment needed for counter-battery fire had to be left in Wellington. Also, because the Wellington dock workers were on strike at the time, the Marines had to do all the load reconfiguration from administrative to combat configuration.