In February, 1942, the 1st and 2nd Separate Battalions were designated 1st and 2nd Marine Raider Battalions
In June, 1942, 2nd Raider Battalion participated in the sea and air battles of Midway Island, with two companies stationed on North Island and Sand Island during the battles. After nearly two weeks, the companies boarded U.S. warships and returned to Pearl Harbor.
On August 7th, 1942, 1st Raider Battalion conducted an amphibious assault landing on the island of Tulagi in the British Solomon Islands.
On August 9th, 1942, two companies from 2nd Raider Battalion embarked at Pearl Harbor aboard two submarines, the SS Argonaut (SS-166) and the SS Nautilus (SS-168), and sailed for the Gilbert Islands. A week later, 2nd Raider Battalion conducted the famed assault landing on Butaritari Island, Makin Atoll, launching rubber raiding boats from the decks of the submarines.
On September 8th, 1942, 1st Raider Battalion conducted a daring raid on the Japanese supply base at Tasimboko, Guadalcanal, beginning a month long fight in the legendary Battle of Guadalcanal. Four days later, on September 12th, they began the Battle of Edson’s Ridge (also known as “Bloody Ridge”) in the successful defense of Henderson Airfield. After another month of fighting, 1st Battalion was withdrawn from the island.
On September 20th, 1942, 3rd Raider Battalion was formed in American and Western Samoa, as well as the Wallis Island Group from elements of the 7th Marine Regiment.
On October 23rd, 1942, 4th Marine Raider Battalion was organized at Camp Joseph H. Pendleton, Oceanside, CA.
On November 4th, 1942, 2nd Raider Battalion conducted an amphibious assault at Aola Bay, Guadalcanal, and begins a 30-day guerrilla mission known as “The Long Patrol.” Over the next thirty days, the battalion participated in six major battles. On December 4th, the battalion returned to friendly lines at Henderson Field. 2nd Raider Battalion left Guadalcanal on December 15th, 1942.
On March 15th, 1943, 1st Marine Raider Regiment was established on Espiritu Santo Island, New Hebrides Islands. The Regiment consisted of Headquarters, 1st, 2nd, 3rd, and 4th Raider Battalions.
On June 21st, 1943, elements of 1st and 4th Raider Battalions participated in the occupation of Segi Point, New Georgia, in the British Solomon Islands. For the next week, the battalions fought in several key battles of the New Georgia campaign, to include Choi River, Viru Village, and Tombe Harbor. In early July, the Raiders consolidated on the island and participated in the Battle of Keruka, Wickham Anchorage. The fighting on New Georgia continued for another two months, with the battalions leaving for good in late August. Both units eventually made their way to New Zealand for Rest and Rehabilitation.