The AAF Response: Tactics, Technology, and Organization

Relative size of equipmentReacting to the ferocity of the U-boat offensive, the AAF developed and adopted tactics that exploited the submarine's need to surface frequently. A submarine emerged daily, usually at night, to recharge batteries, ventilate the boat, and permit crew members to come topside. It often traveled or pursued convoys on the surface because its submerged speed averaged three knots (nautical miles per hour), whereas its surface speed was about fifteen knots, much faster that the ten knots of most merchant ships. Furthermore, submarines remained on the surface to maneuver for attacks and usually to fire their torpedoes or guns before submerging. When Allied escort ships discontinued their search for the submerged U-boats, the Germans could emerge again and circle ahead of the convoy to make another attack. Aerial patrols prevented this maneuver by forcing submarines to dive frequently and remain submerged too long to catch up with the convoys.

German U-boat hit from the air German U-boat sinking Survivors of the German U-boat

By June 1942, the AAF was conducting two broad types of antisubmarine patrols. At the request of the U.S. Navy, AAF crews often escorted Allied convoys to prevent enemy submarines from attacking ships at close range. However, the AAF preferred to take the offensive by flying routine aerial patrols. Searching coastal waters and areas stretching one hundred miles out to sea required precise navigation, reliable communications, and sudden attacks to surprise U-boats traveling on the surface.

Regardless of the type of patrol, aircrews normally flew hundred of hours without sighting a submarine. Boredom could not be allowed to 
dull the crew's reflexes because a successful attack had to take place no more than fifteen to thirty-five seconds after a submarine submerged. Surprise was crucial in sinking or heavily damaging a submarine. Once a target was spotted visually or by radar, the pilot achieved surprise by flying in clouds, with the sun behind the aircraft. Attacking at an angle of 15 to 45 degrees increased the chances of a hit or near-miss. The pilot would fly as low as possible, preferably about fifty feet above the water, and would ideally drop the depth bomb within twenty feet of the submarines pressure hull. The aircrew dropped depth bombs in clusters of six spaces, to fall at fifty- to seventy-foot intervals. As the aircraft passed over, the crew would also fire their machine guns in an effort to damage the submarine and suppress antiaircraft fire.
A specially equipped four-engine Consolidated Vultee B-24 was the AAF's best answer to the submarine threat, particularly in the European-African-Middle Eastern (EAME) theater. The B-24 entered the conflict in the winter of 1942. When the U.S. Navy deployed its escort carriers in mid- to late- 1943, the Liberator provided the most effective means for locating and attacking U-boats operating more than four hundred miles offshore. The U.S. Navy and the Royal Ai Force (RAF) Coastal Command also flew the antisubmarine plane.
Carrying up to 2,500 gallons of fuel, the modified B-24 had an impressive range--about three hours of patrol time after flying a thousand miles from its base. A mission could last sixteen hours, although the average was ten to twelve 

Consolidated B-24 Liberator
hours. The liberator flew day and night, except in bad weather. The heart of the antisubmarine B-24's capabilities was its microwave radar equipment, known as Airborne Surface Vessel Detection ten millimeter (ASV-10) radar. A skillful operator could identify a surfaced submarine at more that forty miles and the conning tower at fifteen to twenty miles. Other special equipment included the absolute altimeter, the magnetic anomaly detector (MAD), and the long-range aid to navigation (LORAN).

The absolute altimeter used a modified microwave radar to determine an aircraft's altitude within ten feet. It replaced the much less exact barometric instrument and permitted aircraft to fly safely as low as fifty feet when attacking submarines. Lower-altitude attacks substantially improved the chances of destroying the target.

The magnetic anomaly detector located any change in the magnetic field of the earth created by a large metal object such as a submarine. MAD-equipped aircraft patrolled areas where submarines had been spotted but had submerged. Crews often combined MAD with a radio sonobuoy, a technique designed to detect the sounds of a submerged submarine. Thus, MAD permitted an intensive air search with a high probability of success.

Aircraft equipped with LORAN received radio signals from three known points, thus allowing navigators to pinpoint their locations within four miles at a range of 1,200 to 1,500 miles from the transmitters. LORAN permitted efficient control of forces converging on submarines for intensive attacks. It also allowed a navigator to guide patrolling aircraft to the most likely location of a surfaced submarine, as determined from intelligence information.

The modified B-24 carried six 500-pound depth bombs; four 20-mm, forward-firing cannons; and six .50-caliber machine guns. In the fall of 1943, several B-24s were fitted with a chin turret housing four more machine guns for increased forward firepower. Depth bombs had shallow fuse settings, and when dropped on a submerging submarine, their blunt shape caused them to sink slowly and explode at a depth of about twenty five feet. Vessels equipped with adjustable depth charges attacked U-boats immersed at greater depths.

Reorganization of the AAF's antisubmarine forces was the final strategy designed in response to the specialized demands of the U-boat threat. Serious disagreements had arisen between the U.S. Navy and the AAF over antisubmarine tactics and the control of AAF forces in U.S. waters. To resolve these conflicts and improve the control and training of AAF antisubmarine forces, Arnold decided to centralize the forces under one organization. On October 15, 1942, the AAF established its Antisubmarine Command under Brig. Gen. Westside T. Larson. The I Bomber Command had been the AAF's primary antisubmarine unit since the beginning of the war, so it provided most of the personnel, aircraft, and equipment for the new command. The new organization introduced unity of command for antisubmarine forces within the War Department. Training, administration, and maintenance also grew more flexible and effective. Although the AAF's antisubmarine groups and squadrons continued under the operational control of the U.S. Navy, they benefited from the reorganization well.