The following information is taken from The Army Ground Forces: The Amphibious Training Center, by Capt. Marshall O. Becker (1946) at this link:
On 9 May 1942, Army Ground Forces was made responsible for the shore-to-shore amphibious training of the twelve divisions trained in the United States. The objective on that date was to train four divisions at Camp Edwards, Massachusetts; six divisions at Carrabelle, Florida; and two at Fort Lewis, Washington. The Camp Edwards training was to be completed between 15 July 1942 and 1 November 1942. The training at Carrabelle was to be initiated at a later date to be set when camp facilities and boats became available. Similarly, the mission prescribed for Fort Lewis was contingent upon the availability of boats. Operations began at Camp Edward. The move to Camp Carabelle started on 6 October 1942. All elements of the Amphibious Training Center had arrived at Carrabelle by 15 October, and preparations were immediately made to receive the first student unit to be trained at the new camp. The new location on the swampy chores of the Gulf Coast of Florida was certainly not an inspiring sight—construction was not completed and fifty yards from the fringe of the camp the casual wanderer found himself in a swampy, tangled, and snake-infested subtropical Jungle.
The period from the arrival of the Center personnel at Carrabelle to the arrival of the first student unit was spent in clearing areas for training, erecting the cargo net towers and other training aids, preparing and revising training schedules, making the new camp liveable, preparing and conducting rehearsals, perfecting plans for the employment of the boat-operating unit, planning for the bivouacking of the next student unit, and reconnoitering for suitable landing beaches and maneuver areas. The first unit to be trained at Camp Gordon Johnston (as the location at Carrabelle was designated on 13 January 1943) was the 38th Infantry Division.