Beginning in the mid 1930’s the Marine Corps began experimenting with amphibious landings. General Holland M. Smith was a leader in this effort and was also searching for ways to incorporate light commando like forces to help with raids on enemy positions, etc.
In June 1941 he personally had picked Lieutenant Colonel Merritt A. “Red Mike” Edson to command a battalion in the First Marine Division and had designated it to serve permanently with the Navy’s APD squadron. Smith began to refer to Edson’s outfit as the “light battalion” or the “APD battalion”. When the 5th Marines and the other elements of the 1st Marine Division moved down to New River that fall, the 1st Battalion remained behind in Quantico with Force headquarters.
Edson’s unit was unique in many ways. In a lengthy August 1941 report, the lieutenant colonel evaluated the organization and missions of his unit. He believed that the APD battalion would focus primarily on reconnaissance, raids, and other special operations-in his mind it was a waterborne version of the parachutists. In a similar fashion, the battalion would rely on speed and mobility, not firepower, as its tactical mainstay. Since the APDs could neither embark nor offload vehicles, that meant the battalion had to be entirely foot mobile once ashore.
To achieve rapid movement, Edson recommended a new table of organization that made his force much lighter than other infantry battalions. He wanted to trade in his 81mm mortars and heavy machine guns for lighter models. There also would be fewer of these weapons, but they would have larger crews to carry the ammunition. Given the limitations of the APDS, each company would be smaller than its standard counterpart. There would be four rifle companies, a weapons company, and a headquarters company with a large demolitions platoon. The main assault craft would be 10-man rubber boats.
The only thing that kept Smith from formally removing the 1st Battalion, 5th Marines, from the 1st Marine Division was the lack of troops to make the regiment whole again. As it was, many units of the division still existed only on paper in the fall of 1941. At the very beginning of 1942, with the United States now at war and recruits pouring into the Corps, Smith wrote the Major General Commandant and asked him to redesignate the battalion.
On 7 January Edson received word that he now headed the 1st Separate Battalion.
The raider battalions soon received first priority in the Marine Corps on men and equipment. Edson and Carlson combed the ranks of their respective divisions and also siphoned off many of the best men pouring forth from the recruit depots.
They had no difficulty attracting volunteers with the promise that they would be the first to fight the Japanese.
On February 16th, 1942 Edson received word that the 1st Separate Battalion had been officially designated the 1st Raider Battalion.