First created in 1912 for duty in Cuba following the Negro Rebellion, the brigade was not activated again until 1941 when it was hastily constructed from the 6th Marine Regiment to garrison Iceland after British forces occupied the country during World War II.

[12] The Marines protected United States sugar plantations in Siboney and El Cobre until late July when the Cuban government was able to clamp down on the revolt.

A British force consisting of 4 Royal Navy warships bloodlessly occupied the country, as the Icelandic government did not resist the invasion.

[16] After the United States entered the war, Iceland signed a defence agreement with the American government allowing U.S. forces to be stationed on the island as part of the Allied occupational garrison.

The USMC hastily assembled the 1st Provisional Marine Brigade in Charleston, South Carolina, to move to Iceland as part of the agreement.

[24] The British commanders distributed the 1st Provisional Marine Brigade throughout camps around the Reykjavik area,[18] to act as an emergency force which could quickly counter any German invasion.

[31] Following the 7 December attack on Pearl Harbor, the men were informed they would be redeployed from Iceland at the beginning of 1942 and would likely see combat in the Pacific Theatre.

[43] The 1st Provisional Marine Brigade encountered lighter resistance on the southern beaches, but nonetheless fought a substantial Japanese force occupying Gaan Point, between the two regiments' landing zones.

[44] Japanese defenders had built fortifications into the point, including Type 41 75 mm Mountain Guns which had gone undetected in U.S. reconnaissance probes,[45] using them to pin down 20 amphibious vehicles supporting the 22nd Marines and slow their advance.

However, thousands of Japanese troops fled to the woods of Guam after the fight, and mop-up operations continued long after the island was declared secure.

The Joint Chiefs of Staff ordered the Marine Corps to ready a 15,000-man division for duty in Korea as a part of the United Nations Command being created there.

It would kick off with an attack by the U.S. reserve units on the Masan area to secure Chinju from the North Korean 6th Division, followed by a larger general push to the Kum River in the middle of the month.

[61] The plan of attack was to move west from positions held near Masan, seize the Chinju Pass, and secure the line as far as the Nam River,[62] and depended on the arrival of the entire U.S. 2nd Infantry Division, as well as three more battalions of American tanks which were en route from the United States.

[71] On 10 August, the Marines picked up the advance,[72] inadvertently encountering the North Korean 83rd Motorized Regiment of the 105th Armored Division, which was caught off-guard and attempted to withdraw.

Beginning at midnight on the night of 5–6 August, North Koreans had begun crossing the Naktong River at the Ohang ferry site, 3.5 miles (5.6 km) south of Pugong-ni and west of Yongsan, carrying light weapons and supplies over their heads or on rafts.

[82][83] At 02:00 on the morning of 6 August, the North Koreans began engaging the 3rd Battalion, U.S. 34th Infantry Regiment, and moved forward after a short fight, attempting to penetrate the lines to Yongsan.

[87] By the morning of 7 August, North Koreans were able to press forward and capture the Cloverleaf Hill and Oblong-ni Ridge, critical terrain astride the main road in the bulge area.

[68][96] They mounted a massive offensive on Cloverleaf Hill and Obong-ni[97] beginning at 08:00 on 17 August,[98] unleashing all available heavy weapons: artillery, mortars, M26 Pershing tanks, and airstrikes.

[108] By 1 September, the 1st Provisional Marine Brigade was down to 4,290 men, having suffered 500 casualties in its month of Korean service,[109] and was preparing to move back to Pusan to evacuate to Japan.

[110] At the same time, the 1st and 2nd Regiments of the NK 9th Division, in their first offensive of the war, stood only a few miles short of Yongsan after a successful river crossing and penetration of the American line.

[111] Division commander Major General Lawrence B. Keiser formed ad hoc units from his support troops but they were not enough to counter the North Korean attack.

[114] On 2 September,[115] Walker spoke by telephone with Major General Doyle O. Hickey, Deputy Chief of Staff, Far East Command, in Tokyo.

[117] He said he had started the 1st Provisional Marine Brigade toward Yongsan but had not yet released them for commitment there and he wanted to be sure that General of the Army Douglas MacArthur approved his use of them, since he knew that this would interfere with other plans of the Far East Command.

[122][124] With help from Marine tank fire, G Company overcame heavy resistance, but this early morning battle for the line of departure delayed the planned attack.

[122] Air strikes, artillery concentrations, and machine gun and rifle fire of the 1st Battalion now caught North Korean reinforcements in open rice paddies moving up from the second ridge and killed most of them.

As the attack progressed, the Marines approached Obong-ni Ridge and the 9th Infantry neared Cloverleaf Hill where they had fought tenaciously during the First Battle of Naktong Bulge the month before.

[129] Assault teams of B Company and the 1st Battalion with 3.5-inch rocket launchers rushed into action, took the tanks under fire, and destroyed both of them, as well as an armored personnel carrier following behind.

[129] The American counteroffensive of 3–5 September west of Yongsan resulted in one of the bloodiest and most terrifying debacles of the war for a North Korean division, according to historians.

[129] Walker had protested in vain against releasing the brigade, believing he needed it and all the troops then in Korea if he were to stop the North Korean offensive against the Pusan Perimeter.

Walker did not feel the inexperienced troops would be effective, and believed the transition endangered the Pusan Perimeter at a time when it was unclear if it could hold back the North Koreans.