Air ASW - World War II Years
Aircraft in the early days of Air ASW primarily relied upon visual lookouts to detect submarines. These patrolling aircraft consisted mainly of Consolidated PBY-5 Catalina seaplanes, smaller aircraft, and various airships (or blimps). Their weapon systems were limited to guns, depth bombs, and rockets.
Of course, having offensive weapons did not necessarily ensure aircraft survivability. In June 1943, Airship K-74 on a night patrol off the Florida coast attacked a surfaced German submarine. The airship was shot down in the ensuing gun duel. The submarine, U-134, was forced to return to base. As the submarine struggled back home, it survived two subsequent attacks but was finally sunk by British bombers in the Bay of Biscay.
In the European theater, ASW aircraft patrolled from airfields in Iceland and French Morocco as well as various European airstrips. Coverage of the North Atlantic came from Argentia located in Newfoundland, Canada while patrols from Natal, Brazil watched the South Atlantic. Aircraft operated from many sites within the continental U.S. as well as Puerto Rico, Cuba, Trinidad, and Panama to cover the Caribbean and the Gulf of Mexico.
The Japanese submarine threat was countered by aircrews operating from Australia and the many islands of the South Pacific, Hawaii, and the Aleutians. Protection of the West Coast was provided mainly from airfields in San Diego and Moffett Field, California. Interestingly enough, seaplanes operating from distant bases were periodically refueled at sea by submarines designed to deliver aviation gasoline.
World War II-vintage diesel submarines still had to surface during the night to re-charge their spent batteries. ASW aircraft countered these submarine nighttime operations with searchlights, flares and radar systems. This worked for a while until the submarine community responded with electro-magnetic sensors to detect aircraft radar emissions, snorkels to minimize their exposed hull surfaces, and radar decoys. Other ASW aircraft sensors employed during World War II included MAD and sonobuoys. Additionally, aircraft went through many different paint camouflage schemes to mask their appearance not only from hostile submarines, but also from enemy aircraft, ships, and coastal land watch.
Prior to the attack on Pearl Harbor, Catalina aircraft began experimentation with Magnetic Anomaly Detection (MAD) systems. A Catalina operating from Quonset Point, Rhode Island successfully demonstrated the MAD system by detecting a submarine during the initial testing. Additionally, ten days after the Pearl Harbor attack, the Naval Research Laboratory (NRL) satisfactorily demonstrated a duplex switch which allowed a Catalina radar system to transmit and receive electromagnetic pulses without using a cumbersome secondary antenna system.
Although sonobuoys had been developed in 1941, the concept was not fully endorsed. Meanwhile, blimps were wasting time and weapons after detecting multiple MADs of sunken ships and old wrecks. They needed a sensor to validate and corroborate MAD contacts. Hence the passive sonobuoy concept was "dusted off" the shelves for use by the airships. In February 1942, the Navy's Coordinator for Research and Development requested the National Defense Research Committee (NDRC) to develop an expendable radio sonobuoy which could be used by lighter-than-air (LTA) aircraft.
In March 1942, the practicality of sonobuoys was demonstrated off New London, Connecticut as a K-5 blimp detected the propeller sounds of the submarine S-20 at maximum distances of three miles. Radio reception of the signals, however, was limited to five miles. In October 1942, the Bureau of Ships began sonobuoy procurement by purchasing 1,000 sonobuoys and 100 ASW receivers.
Later in June, Project Sail was formally established at Quonset Point for conducting MAD system research and testing. Sponsored by the Naval Ordnance Laboratory and the NDRC, the promising results conducted with airships and an Army B-18 resulted in the procurement of 200 MAD units. The successful deployment of a working MAD system consequently led to the requirement for a weapon system to attack submarines. Detection of MAD signatures occurs after the aircraft has flown over the submarine. Hence, a retro-rocket weapon was designed to fly backwards a short distance to the approximate position where the MAD anomaly was detected and release a depth bomb. These retro-rockets were designed by the California Institute of Technology using a Catalina aircraft. They were installed a year later to complement the MAD gear in VP-63 aircraft. In January 1944, VP-63 aircraft began patrolling the Straits of Gibraltar. The aircraft threat and the associated MAD gear effectively closed submarine daylight transits through this narrow channel. Five weeks later, VP-63 detected the MAD signature of a submarine attempting to cross the straits. Attacked by Catalina retro-rockets, the submarine (U-761) was later sunk with the assistance of two other ships and additional aircraft.
Air ASW efforts were not just limited to improved sensors; improvements in ASW aircrafts were also examined. In June 1942, Igor Sikorsky's VS-300 helicopter was inspected by naval personnel and recommended for ASW and life-saving operations. The following month, the Bureau of Aeronautics issued a Planning Directive calling for the procurement of Sikorsky's helicopters. In April 1943, the Commander-in-Chief of the U.S. Fleet established a joint board to evaluate helicopters for ASW. Later that June, helicopters were recommended to carry radar and dipping sonar systems and to use these primitive helicopters as a hunter platform rather than a killer unit. By January 1944, it was determined that a helicopter with ASW capability would be limited to coastal waters until flight performance improvements could be made.
Meanwhile, in February 1943, a Letter of Intent (LOI) was sent to the Lockheed Vega Airplane Division for the development of two XP2V-1 patrol planes. This would be the initial development of the U.S. Navy's patrol plane workhorse through the early 1960's, the Lockheed P-2V Neptune.
By the end of the war, Navy and Marine aircraft sank 13 submarines. Working with other forces, they sank 26 submarines (6 Japanese, 20 German).
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