Fighting the U-boats

Aircraft & Air Forces

American Air Forces

The Battle against the U-boat in the American Theater

December 7, 1941 - September 2, 1945


Admiral Doenitz recognized that improvements in Allied tactics and weapons had turned the tide of war against the German submarines. He noted in a memorandum dated June 1943:

"The war at sea is at present characterized by a decrease in the victories of our U.S. Navy against enemy merchant shipping. The principal exponent of this type of warfare, the submarine, is limited in operational capacity by the ever growing strength of the enemy's anti submarine defenses and in particular by the enemy Air Force, using as yet unknown equipment and weapons."

The "unknown" equipment and weapons owed their existence at least in part to the 1st SeaSearch Attack Group which General Arnold established on 17 June 1942, at Langley Field, Hampton, Virginia. The group engaged in the development of equipment and tactics best suited for aerial anti submarine warfare. Among the devices that the group helped develop or test were the absolute altimeter, the magnetic anomaly detector (MAD), the radio sonic buoy, improved airborne depth charges, longrange navigation, and airborne microwave radar.

The absolute altimeter used a modified microwave radar to determine an aircraft's exact altitude to within 10 feet (3 m). This altimeter, replacing the less accurate barometric instrument, permitted aircraft to fly safely as low as 50 feet (15 m). The low altitude attack substantially improved the chances of destroying the target. This device was standard equipment on USAAF anti submarine aircraft by 1943.

The magnetic anomaly detector (MAD) operated by sensing a change in the magnetic field of the earth, an anomaly that could be produced by the steel hull of a submarine. Aircraft outfitted with this device would patrol in an area where a submarine had been spotted but had submerged. Combined with the use of a radio sonic buoy to listen for the sounds of a submarine, the MAD permitted an intensive search with a high probability of success. Another important development was the use of LORAN (long range aid to navigation). The aircraft received radio signals from three known points, allowing the navigator to pinpoint his location to within four miles (6.4 km) at a range of 1,200 to 1,500 miles (1,931 to 2,414 km) from transmitters. LORAN permitted efficient control of converging forces. LORAN coverage extended over the Eastern Sea Frontier, Gulf Sea Frontier, and most of the Caribbean Sea and North Atlantic Ocean.

A B-24 very-long-range bomber

The 1st SeaSearch Attack Group also helped develop an effective depth bomb with shallow fuse settings for about 25 feet (7.6 m). Eventually, the Americans and British developed a blunt depth bomb that sank slowly and exploded at the desired depth to destroy the submarine. This depth bomb became standard in early 1943.

Perhaps the most important task of the 1st SeaSearch Attack Group was to develop techniques for using Airborne Surface Vessel Detection (ASV) radar to find surfaced submarines. The radar that eventually went into production was 10centimeter wave equipment, known as ASV10. The British had developed a long wave ASV radar and used it to find submarines in 19411942. As early as March 1942, the I Bomber Command had four B-18's outfitted with the long wave radar sets, but the Germans outfitted their submarines with a long wave radar detector that effectively countered the British radar. The United States quickly developed the microwave radar, which the Germans never effectively countered. The first microwave sets were hand manufactured and delivered to the 1st SeaSearch Attack Group in June 1942. By February 1943, a skilled radar operator could identify surfaced submarines at more than 40 miles (64 km) and even the conning tower of a boat running decks awash at 15 to 30 miles (24 to 48 km).

Radar sets were notoriously unreliable and difficult to maintain, and scientists assigned to the 1st SeaSearch Attack Group found much of their time consumed by seminars in the field on basic functions and maintenance of equipment. Consequently, the USAAF established a unit in the group to train ground personnel in its proper maintenance.

Initially the ASV10 radar sets were placed on B-18 medium bombers flying anti submarine patrols. Some 90 B-18's carried the equipment by the end of June 1942, but the Allies needed the microwave radar on the B-24. Equipped with auxiliary fuel tanks, microwave radar, and a powerful search light, this very long range bomber was ideal for extended anti submarine patrols. The USAAF outfitted its first two microwave radar equipped B-24's in September 1942, and the 1st SeaSearch Attack Group acquired a squadron of B-24's in December.

Using the B-18's and B-24's assigned to it, the 1st SeaSearch Attack Group trained combat crews in the tactical employment of new equipment. In general, the USAAF employed three broad types of anti submarine operations: (1) routine aerial patrol of waters in which an enemy threat might exist; (2) air escort or coverage of convoys within range of land based aircraft; and (3) intensive patrol of an area in which one or more submarines had been spotted, an operation the USAAF termed a "killer hunt" (in contrast to the U.S. Navy expression "hunter killer"). At various times, each of these operational tactics had its place in the anti submarine war.

Early in the war, the USAAF usually used the aerial patrol to restrict and hamper enemy operations. Such flying required precise navigation and reliable communications, and the crew had to identify surface craft accurately to avoid attacks on friendly vessels. However, an air crew on routine anti submarine patrol could fly hundreds of hours without sighting a submarine. As most German submarines withdrew in the summer of 1942 from American waters, the routine patrols, with virtually no chance of spotting an enemy submarine, became the nemesis of the Army air crews.

Aerial escort of convoys came close to being as resented as the routine patrols. The USAAF considered these anti submarine operations to be primarily defensive in character, but they were absolutely essential to prevent enemy submarines from attacking convoys. After the institution of the coastal convoy system on 15 May 1942, the U.S. Navy frequently called on the USAAF to protect convoys, initially between Key West, FLorida and the Chesapeake Bay, later in the Caribbean.

Although convoy duty was essential, the USAAF preferred the offensively oriented killer hunt. This tactic most effectively used the newly developed sonic buoys, magnetic anomaly detectors, and microwave radar. A patrolling aircraft that spotted and unsuccessfully attacked a German submarine would radio its location to its home base. The information would be passed on to U.S. Navy authorities, who would dispatch a force of ships and aircraft to maintain contact with the submarine and attack it as the opportunity arose.

The killer hunt took large numbers of aircraft and surface vessels from normal convoy escort and patrols, and the U.S. Navy did not regularly employ it until mid 1943. The escort aircraft carriers used this tactic very effectively against German submarines, including the "milch cows." The escort carriers coupled with ULTRA allowed the Allies to attack not just defensively, as in convoy escort, or fortuitously, as in aerial patrol, but also actively by seeking out the enemy submarines. Between June and October the escort carriers, guided by ULTRA intelligence, located and destroyed nine of the ten refueling submarines operating in the Atlantic Ocean.

The first killer hunt to result in a destroyed submarine occurred much earlier in the Gulf Sea Frontier on 10-13 June 1942. A German submarine, U-157, sank a ship north of Cuba on the night of 10 June. Within three hours, a radar equipped B-18 out of Miami, Florida was patrolling in the vicinity and early on the 11th unsuccessfully attacked the surfaced submarine. Other USAAF B-18's in the area contacted and attacked the submarine several times over the next two days. Meantime, five U.S. Navy ships out of Key West, Florida sailed to the area. Making sound contact with the submerged submarine on the 13th, the U.S. Navy crews sank it with depth charges.


The killer hunt involved close cooperation among the operational forces of the USAAF and the U.S. Navy. Unfortunately, this cooperative attitude did not lessen inter-service rivalry concerning organization, control, and use of land based aircraft. The USAAF deemed the U.S. Navy's continuing operational control of its aircraft an intolerable situation, especially since the U.S. Navy kept most of the anti submarine Command's aircraft on endless patrol off the East Coast. To meet the USAAF's objections and achieve better control and coordination between the services, U.S. Army Chief of Staff, General George C. Marshall, proposed in April 1943 a centralized anti submarine organization under the Joint Chiefs of Staff. Admiral King rejected this proposal but on 20 May 1943, established the Tenth Fleet, a U.S. Navy command with jurisdiction over all anti submarine activities. Although the Tenth Fleet brought needed order to the American anti submarine effort, Army leaders remained unhappy because the AAFAC remained under the U.S. Navy's operational control. Besides, in the opinion of General Arnold and the USAAF leadership, the U.S. Navy appeared to be duplicating the USAAF's efforts. By this time, the U.S. Navy was receiving large numbers of B-24's to use on anti submarine patrols.

On 9 July 1943, after several meetings, the Army and the U.S. Navy agreed that the USAAF would withdraw from anti submarine operations. In accordance with this agreement, the USAAF by 6 October turned over 77 B-24's configured with anti submarine equipment to the U.S. Navy in return for an equal number of unmodified B-24's from the U.S. Navy allocation. On 31 August the USAAF re designated the AAFAC as the I Bomber Command and assigned it to the First Air Force, re designating the anti submarine squadrons as heavy bombardment squadrons. The 25th and 26th anti submarine Wings were disbanded, but two anti submarine groups overseas, the 479th anti submarine Group at Dunkeswell, England and the 480th anti submarine Group at Port Lyautey, French Morocco, continued operations into October 1943 before being inactivated. Thus, the USAAF ended its anti submarine mission, mostly disdained in spite of its strategic significance as temporary and secondary to the USAAF's responsibilities as a strategic bombing force.

German submarines sank fewer than 20 ships in the Atlantic Ocean between September 1943 and the end of the war. Still, the submarine threat tied down large Allied naval and air forces. Hitler recognized the Atlantic Ocean as his first line of defense in the West and the danger of the anti submarine forces if they should be released to undertake other military tasks against Germany. Thus, the submarines operated until the end of World War II, even returning in small numbers from time to time to the Caribbean Sea or the East Coast of the United States.


Statistics underline the menace of the German submarine offensive. Submarines sank over 2,600 Allied ships, totaling about 15 million tons. Germany built 1,162 submarines, of which 785 were sunk, 156 surrendered at the end of the war, and the rest scuttled or otherwise destroyed. German submarines operated between September 1939 and May 1945 not only in the North Atlantic and American waters but also in the South Atlantic, Caribbean Sea, Gulf of St. Lawrence, Mediterranean Sea, Indian Ocean, Kola Inlet in North Russia, as well as around the Cape of Good Hope and along the coasts of Australia and Brazil.

During the Battle of the Atlantic the Canadians and the British sank most of the German submarines destroyed in the American Theater. The U.S. Navy and the USAAF cooperated with Canadian and British forces to stifle the German submarine offensive off the East Coast, in the Gulf of Mexico and the Caribbean Sea, and in the North Atlantic Ocean. Since the Japanese made relatively few submarine attacks off the West Coast, the USAAF contributions there mostly amounted to reassuring the public and governmental officials that anti submarine operations were in place to defend shipping and deter the enemy.

During the war, increasingly effective anti submarine air patrols resulted from deployment of modified B-24's, development of various finding aids and other technological advances, and experience in the specialized tactics of hunting and attacking submarines. After the war, Admiral Doenitz cited the radar equipped very long range B-24 as a decisive factor in the defeat of the German submarines in the North Atlantic. The USAAF and the U.S. Navy explored the best tactical combination of radar, depth bombs, and the magnetic anomaly detector in the aerial search for submarines. Working together at the tactical level, the two services conducted a successful offensive action against enemy submarines, helping to turn the tide of submarine war against the German submarine fleet within about 18 months.

As part of the overall Allied anti submarine effort, the USAAF significantly affected the outcome of the campaign. In terms of the force available, the USAAF increased its anti submarine force from a few obsolete observation aircraft, medium bombers, and B-17's, all without radar, to 187 operational B-24's, 80 B-25's, 12 B-17's, and seven Lockheed B34 Ventura’s, most equipped with microwave radar and other detection equipment. These 286 aircraft were assigned to the Army Air Forces anti submarine Command when, on 24 August 1943, the USAAF withdrew from anti submarine operations in the American Theater. In this theater, USAAF aircraft flew over 135,000 operational combat hours on anti submarine patrols. Altogether, the USAAF participated in 96 attacks on German submarines between 7 December 1941 and 24 August 1943. These statistics do not include the contribution of the AAFAC in the anti submarine Campaign, European-African-Middle Eastern Theater, nor of the Army Air Force's bombers which frequently attacked the German submarine bases and sometimes sank submarines anchored in their berths.

The USAAF's anti submarine campaign harassed the Germans to the point of ineffectiveness. Even the efforts of the small unarmed Civil Air Patrol aircraft in the shallow coastal waters contributed to this outcome. The German policy from the beginning of the war was to withdraw from areas that became too dangerous because of heavy aerial patrols. By May 1943, Germany had lost the strategic initiative in the Battle of the Atlantic. Aircraft had forced the enemy to submerge so frequently and stay down for such extended intervals that their targets escaped and Uboat activity became so handicapped that the returns barely justified the expense.

Suggested Reading

1. Wesley F. Craven and James L. Cate, editors., THE ARMY AIR FORCES IN WORLD WAR II (Chicago: University of Chicago Press, 1948, reprint Washington DC: Office of Air Force History, 1983).

2. Michael Gannon, OPERATION DRUMBEAT (New York: Harper & Row Publishers, 1990).

3. Gunter Hessler, GERMAN NAVAL HISTORY: THE UBOAT WAR IN THE ATLANTIC, 1939-1945 (London: Her Majesty's Stationery Office, 1989).

4. Terry Hughes and John Costello, THE BATTLE OF THE ATLANTIC (New York: The Dial Press/James Wade, 1977).

5. David Kahn, SEIZING THE ENIGMA (Boston: Houghton Mifflin Co., 1990)

6. Montgomery C. Meigs, SLIDE RULES AND SUBMARINES: AMERICAN SCIENTISTS ANDSUBMARINE WARFARE IN WORLD WAR II (Washington DC: National Defense University Press, 1990).

7. Samuel Eliot Morison, HISTORY OF THE UNITED STATES NAVAL OPERATIONS IN WORLD WAR II (Boston: Little, Brown and Co., 1947).

8. John Winton, ULTRA AT SEA (New York: William Morrow and Co., 1988).

9. William T. Y'Blood, HUNTERKILLER (Annapolis: Naval Institute Press, 1983).

The Battle against the U-boat
in the American Theater

   Part I
   Part II
   Part III