On 18 April 1944, the 1st Provisional Marine Brigade was activated, this time at Guadalcanal and placed in reservefor a time. commanded by Brigadier General Lemuel Cornick Shepherd. In July, it was moved to the Marchall Islands for a planned invasion of Guam, an island under the control of the Empire of Japan . This much larger brigade was built around the 4th and 22nd Marine Regiments with supporting units, and comprised 9.886 Marines. The brigade was assigned to III Amphibious Corps , a force almost 67.000 strong, in anticipation of a 15 July invasion of Guam’s southern beaches, in conjunction with a northern landing by the Army’s 4.500-man 305th Infantry Regiment, 77th Infantry Division nickname “Statue of Liberty” . The brigade commenced training at Guadalcanal in conjunction with the 3rd Marine Division, “Fighting Third” . At the end of the battle the division had sustained 677 Marines killed, 3,626 wounded and 9 missing. Then, in early July, the two formations staged through the Eniwetok in preparation for the invasion.On 21 July at 08:32 the 22nd Marines landed on beaches around Agat while the 4th Marines under command of Lieutenant General Alan Shapely landed at Bangi Point to the north. Shapely was a United states Marine Corps officer who survived the sinking of the USS Arizona during the attack on Pearl Harbor, and went on to serve with distinction in the Pacific Theater and later in the Korean War. He was awarded the Silver Star for his gallantry on December 7, 1941, and later the Navy Cross for his extraordinary heroism during the Battle of Guam. Shapely died May 13, 1973 (aged 70) in Bethesda Maryland
Opposing the U.S. landings were 22,000 Japanese troops stationed on the island. The most intense fighting struck the other units of III Amphibious Corps to the north , which held through heavy Japanese counterattacks. 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. Japanese defenders had built fortifications into the point, including Type 41 75 mm Mounyain Guns which had gone undetected in U.S. reconnaissance probes, using them to pin down 20 amphibious vehicles supporting the 22nd Marines and slow their advance. The 22nd Marines subsequently spent most of the day capturing the point against stiff Japanese resistance. Their 1st Battalion was eventually able to capture Agat, and the 2nd Battalion took Mount Alifan, 1,000 metres (3,300 ft) inland. In the meantime, the 1st Battalion of the 4th Marines” The China Marines” , took Bangi point with support from their 3rd Battalion, nickname “Thundering Third The Bull”. They then began an advance to Mount Alifan but were delayed by fierce Japanese resistance inland. At nightfall the Japanese mounted a large, coordinated counterattack which was unsuccessful. By the end of the day, the 4th and 22nd Marines were holding positions 2,000 metres (6,600 ft) into the island along a 4,500-metre (14,800 ft) front. The 305th Regimental Combat Team supported the Marines for several days before rejoining the rest of the 77th Infantry Division to the north. The 1st Brigade was 7 miles (11 km) south of the 3rd Marine Division and 77th Infantry Division landing zones to the north at Asan On 25 July, the two forces cut off Orote Peninsula between the two landing zones, and the brigade turned west and cleared the peninsula until 29 July against heavier resistance, killing some 2,500 Japanese. It advanced north in a sweeping motion with the 4th Marines on the right, west flank and the 22nd Marines on the left, east flank, until reaching the forces on the northern beach landings.
By 28 July, the 3rd Marine Division and 77th Infantry Division under Lieutenant General Andrew Davis Bruce had formed a continuous flank and were advancing north. General Andrew Davis Bruce died July 28, 1969 (aged 74) North Carolina, On 6 August, the brigade joined them on the left, western flank. Here, Japanese forces staged last stands in their remaining fortifications, and holdouts on Mount Santa Rosa were cleared on 8 August, Ritidian Point on August 10, and Patti Point the same day. Pati Point is the easternmost point of Guam. The island was declared “officially” secure at 11:31 on 10 August, after 11,000 Japanese dead had been counted. 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. By V-J Day, the island had cost the Japanese 18.400 killed and 1.250 captured, and the Americans 1.700 killed and 6.000 injured. The 1st Provisional Marine Brigade, however, only assisted in mop-up operations for a month. The 4th Marines moved along the north coast while the 22nd Marines patrolled inland to the south.
On 9 September 1944, the brigade was disbanded and its elements were moved to Guadalcanal where the new 6th Marine Division, the Striking Sixth was forming. The Sixth division was credited with over 23,839 enemy soldiers killed or captured, That division was activated on 25 September 1944. Most of the Provisional Marine Brigade units were transferred to the command of the 6th Marine Division. The 29th Marine Regiment was added to form the division.
The island was declared “officially” secure at 11:31 on 10 August, after 11,000 Japanese dead had been counted. 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. By V-J Day, the island had cost the Japanese 18,400 killed and 1,250 captured, and the Americans 1,700 killed and 6,000 injured. The 1st Provisional Marine Brigade, however, only assisted in mop-up operations for a month. The 4th Marines moved along the north coast while the 22nd Marines patrolled inland to the south.