The 40th Bomb Group was activated April 1, 1941, at Borinquen Field, Puerto Rico. Consisting of four squadrons (the 25th, 44th, 45th and 395th), it engaged in anti-submarine duty over the Caribbean, using Douglas B-18 Bolo bombers (derivatives of the DC-3/C-47). In May 1942, the group was transferred to the Panama Canal Zone, where it received Boeing B-17 Flying Fortresses and Consolidated B-24 Liberators for further sub-patrol operations.