On 7 March 1942, the Navy blimp K-5, cruising over waters south of New London, Connecticut, used a new device to detect the submarine S-20, then running completely submerged. Something called a sonobuoy—a floating sonar that transmitted acoustic signals to a receiver on board the aircraft— made it possible. Improved sonobuoys were used extensively from then through the end of World War II, and 50 years later greatly enhanced sonobuoys remain one of the prime submarine detectors available to sub-hunting aircraft.
During July 1941, under the aegis of three universities—Columbia, Harvard, and California—three new naval antisubmarine laboratory research activities were established to help find ways to combat the German U-boats that had enjoyed such free rein during the early part of the war. The shipping losses for 1940 averaged about 80 per month, and this had increased to 143 per month by the end of 1942.
The successful test came only eight months after the establishment of Columbia University’s antisubmarine research laboratory at Fort Trumbull, New London, Connecticut.
Russell L Mason! a civilian engineer and a 1941 charter member of Columbia’s New London Laboratory, was on board the blimp during the initial test; he stayed involved with sonobuoy development for the next 35 years. In 1984, he observed that any list of technological developments that changed the face of naval warfare usually included radar, aircraft, submarines, radio, and computers—but that sonobuoys were often omitted. Today, however, the role of the sonobuoy in antisubmarine warfare is acknowledged universally.
Columbia’s efforts were concentrated at New London; Harvard’s research facility was at Cambridge, Massachusetts; and the University of California began work at the Navy Radio and Sound Laboratory at Point Loma, San Diego, California. Scientists from the laboratories ranged far afield throughout the war.
The three laboratories owed their existence to a decision by Secretary of the Navy Frank Knox, who on 27 June 1940 asked the National Academy of Science to appoint a committee to advise him on the scientific aspects of defense against submarines and the adequacy of the Navy’s preparations.
In January 1941, the committee’s recommendations included the need for immediate broad scientific and engineering investigations for the development of equipment and methods involved in submarine and subsurface warfare. The committee further emphasized the importance of the selection and training of the personnel who would operate the underwater sound equipment.
Late in March 1941, the recommendations reached the General Board of the Navy. On 10 April 1941, Admiral S. M. Robinson, Chief of the Bureau of Ships, sent a letter to Dr. Vannevar Bush, Chairman of the National Defense Research Committee (NDRC), asking him to undertake an investigation of submarine detection. The commands to be supported by the laboratories included submarine and destroyer forces in the Atlantic and Pacific, Army Air Force, Royal Canadian Air Force, and the Fleet Air Arm of the Royal Navy.
James Phinney Baxter III, the historian of the Navy’s Office of Research and Development, in his 1946 Pulitzer Prizewinning official history Scientists Against Time, said of the sonobuoy: “Developed with infinite skill and thoroughness, and sent into operation through most intimate cooperation between the New London Laboratory and Air Force, Atlantic Fleet, the expendable sono-radio buoy became one of the outstanding developments of the war.”
The earliest proposal for an expendable sonic buoy was made by Dr. P. M. S. Blackett, a senior British physicist broadly involved in the war effort, who in May 1941 wrote a memorandum proposing a detector buoy astern of convoys to detect shadowing or trailing enemy submarines. Some of Bush’s scientists apparently learned about the proposal while in Great Britain on an exchange mission concerning antisubmarine devices.
The British government, under the auspices of NDRC, subsequently requested the Radio Corporation of America (RCA) to develop a medium-life, ship-launched, convoy-type radio sonobuoy. The New London Laboratory was responsible for the testing, and by 12 September 1941, RCA had units ready for testing at sea. The electrical performance of the buoy was excellent, but the Navy rejected it because of its limited acoustic range. The remaining experimental models were used to great advantage, however, during the development of the aircraft-type buoy.
In December 1941, the laboratory was asked to develop a hydrophone for use with the harbor protection radio sonobuoy authorized by the Navy. Efforts were successful, and a large quantity of these devices were manufactured under Navy contract and later used extensively at advanced bases.
In February 1942, the Navy’s interest in the sonobuoy was rekindled by a need to improve the ASW capabilities of coastal- patrol blimps, which were using early versions of magnetic anomaly detector (MAD) equipment to distinguish live submarines from submerged wrecks along the coast. The New London Laboratory investigated both a dropped radio sonobuoy and a hydrophone towed from a blimp.
All of this led to the breakthrough on 7 March. The blimp did not actually make the first drop. Two modified RCA buoys, left over from previous tests, were placed in the water by a launch. The sonobuoy was able to detect the submarine S-20’s underwater sounds at ranges up to three miles. In turn, the receiver on the K-5 picked up the sonobuoy transmissions easily while cruising within five miles. This particular test moved the sonobuoy into the first rank of detectors.
Mason operated the receiver on board the blimp K-5; he, J. C. McNary, and V. V. Graf submitted the test report. During his career, Mason received 16 patents, including one for the original airborne sonobuoy.
Not long after, the U.S. Army Air Corps, heavily engaged in antisubmarine flights off the East Coast, became interested in the sonobuoy. As a result of the interest and encouragement by a Colonel Dolan of the Sea Search Group operating out of Langley, Virginia, sonobuoys were altered at New London for aircraft instead of blimp delivery. By 25 July 1942, an aircraft had successfully launched a sonobuoy.
Mason, reflecting on this episode in 1984, said: “[By] . . . August 1942, Colonel Dolan expended sonobuoys in actual offshore operations against U-boats. The success . . . caused the Army to order 6,410 buoys in late 1942.”
Additional Navy blimp tests had proved successful; sonobuoys were ordered in quantity in mid-1942; and operations employing sonobuoys began in August. More than 400 experimental buoys and 30 receivers were contracted to the Emerson Radio and Phonograph Corporation, General Electric Company, and the Freed Radio Corporation.
By June 1943, the expendable radio sonobuoy had been officially approved by the Navy for use on all planes and blimps engaged in antisubmarine warfare. Later in 1944 and 1945, sonobuoy use extended to include air-sea rescue operations for airmen downed in the Pacific.
Columbia University’s final report ineludes an individual description of all the New London Laboratory’s projects, a summary of patent reports, and an index of documents for the period 15 September 1941 to 30 June 1945. The laboratory undertook more than 80 projects during this period.
Samuel Eliot Morison identified the importance of the sonobuoy to the Normandy invasion in The Two-Ocean War: “[An] entire portion of the channel was inspected by a plane every 35 minutes. All had microwave radar and sonobuoys to drop . . . not one of the 58 U-boats Dönitz alerted . . . got near the invasion area.”
The 26 months from March 1942 to the Normandy invasion in June 1944 was a comparatively short time to develop, manufacture, and field what turned out to be one of the decisive tools in the confrontation with the U-boats. They had come a long way since Mason tested the first units by dropping them from a Thames River bridge in New London and a Connecticut River bridge in Middletown—on one occasion leading a Federal Communications Commission radio monitoring site to suspect clandestine spy transmissions.
The 29 October 1948 issue of the New London Underwater Sound Laboratory biweekly Bulletin contained the first account of the adventures of the three New London Laboratory civilian engineers whose field work with the sonobuoy led them into combat areas. Mason’s tenure with the sonobuoy during the war extended from February 1942 until June 1945. His overseas assignments carried him to every continent except Asia. The other two members of this triumvirate, Russell Lewis and Walter Clearwaters, came from Purdue University and were on board and involved with sonobuoys by 1943.
Lewis was assigned to the group that introduced the sonobuoy to the Navy. In early summer 1943—accompanied by Mason—his first field trip took him to Argentia, Newfoundland, where VB-103 was preparing for antisubmarine escort duty in the mid-North Atlantic that would close a gap hitherto unprotected from the air. The squadron’s aircraft were equipped with radar, long-range navigation (Loran), guns, depth charges—and sonobuoys. During their time with the squadron both men participated in many 14-16 hour patrols to the middle of the North Atlantic and back, flying anti-submarine sweeps ahead of the convoys.
By September, Lewis had helped Fleet Air Wing 7 prepare for sweeps over the Bay of Biscay and the English Channel. Following this, he went on to Hawaii, and by November was in Bermuda. January 1944 found him flying ASW patrols from the escort carrier USS Block Island (CVE-21) off Portugal and the Azores. On 29 May 1944, the carrier was torpedoed by the German submarine U-549—later sunk herself by the carrier’s escorts—and Lewis spent several hours in the water along with the other survivors before being picked up by a destroyer and taken to Casablanca. His globe trotting continued until March 1945. He spent more than 2,500 hours in the air on tests, travel, and operations. He made 19 transoceanic flights, survived four crashes, and was awarded a Navy commendation.
In June 1943, Clearwaters and Price Fish, also from the New London Laboratory, went to Iceland to install sonobuoy equipment in the planes of Patrol Squadron 63 in preparation for combat operations in European waters. They accompanied the squadron to South Pembroke, Wales, and flew on submarine-hunting missions.
Back in Iceland in late September, Clearwaters participated in an antisubmarine flight with the Royal Canadian Air Force on which the crew successfully engaged a German submarine, providing an opportunity for Clearwaters to use sonobuoys in the air attack. His next stop was the escort carrier USS Bogue (CVE-9), and then it was on to Casablanca. In early 1945 he completed his sonobuoy work as a member of the laboratory team that participated in extensive tests off Fort Lauderdale, Florida.
By war’s end in summer 1945, the Navy had ordered 150,000 expendable sonobuoys and 7,500 receivers. The Royal Canadian Air Force, the Royal Air Force, and the Fleet Air Arm of the Royal Navy also employed the equipment.
The work on the sonobuoy concluded with the administrative changes in the Laboratory that took place in 1945. There was some continuing industrial interest, and the Naval Air Development Center at Warminster, Pennsylvania, evolved as a focus for the sonobuoy during the 1950s. The United States, Canada, and Great Britain continued to pursue their interests in airborne antisubmarine warfare. Sonobuoys were standardized among the three countries, and later joined by Australia and New Zealand.
Today, the literature on antisubmarine warfare reflects the continuing recognition of the importance of the sonobuoy. In 1989, Captain W. T. T. Pakenham described sonobuoys as “ ... a most valuable method of harnessing the mobility of aircraft for antisubmarine warfare.” He also included reference to the important use of sonobuoys in conjunction with helicopters. Much of the success of the ASW helicopter can be traced to the effectiveness of current-day sonobuoys.
Fifty-two years later, the lineal descendants of this World War II development are still on the front line.