 Forces assigned included the 1st Cavalry Division; No.73 Wing RAAF, providing close air support; the 592nd Engineer Boat and Shore Regiment (EBSR); the US Marines' 1st Amphibious Tractor Battalion; and US Naval Construction Battalions ("Seabees") to build the naval base—a total of 45,000 personnel.However, on 23 February 1944 three Fifth Air Force B-25 Mitchell bombers flew low over Los Negros.