the sound to the ship, allowing the crew to make precise position fixes by using triangulation. In 1931, the Coast and Geodetic Survey proposed the replacement of crewed station ships with "radio-sonobuoys", and placed the new buoys in service beginning in July 1936. These buoys weighed , could be deployed or recovered by Coast and Geodetic Survey ships in five minutes, and were equipped with subsurface hydrophones, batteries, and radio transmitters that automatically sent a radio signal when their hydrophones detected the sound of a ranging explosion. These "radio-sonobuoys" were the ancestors of the sonobuoys that began to appear in the 1940s. The damage inflicted upon the Allies by German U-boats during World War II made the need for sonar a priority. With millions of tons of shipping being sunk in the Atlantic, there was a need to locate submarines so that they could be sunk or prevented from attacking. Sonar was installed on a number of ships along with radar and high-frequency direction finding ("Huff-Duff") to detect surfaced submarines. While sonar was a primitive system, it was constantly improved. Modern anti-submarine warfare methods evolved from the techniques devised for the movement of convoys and battle groups through hostile waters during World War II. It was imperative that submarines be detected and neutralized long before the task group came within range of an attack. Aircraft-based submarine detection was the obvious solution. The maturity of radio communication and sonar technology made it possible to combine a sonar transducer, batteries, a radio transmitter and whip antenna, within a self-contained air-deployed floating (sono)buoy. Early sonobuoys had limited range, limited battery life and were overwhelmed by the noise of the ocean. They first appeared during World War II, in which they first were used in July 1942 by RAF Coastal Command under the code name 'High Tea', the first squadron to use them operationally being No. 210 Squadron RAF, operating Sunderlands. They were also limited by the use of human ears to discriminate man-made noises from the oceanic background. However, they demonstrated that the technology was viable. With the development of better hydrophones, the transistor and miniaturization, and the realization that very low frequency sound was important, more effective acoustic sensors followed. The sonobuoy went from being an imposing tall, diameter sensor to the compact suite of electronics it is today. The advancement in sonobuoy technology aided the development of aircraft such as the