GHz (wavelengths of 10 to 1 cm). Centimetric radar enables the detection of much smaller objects and the use of much smaller antennas than the earlier, lower frequency radars. A radar with a wavelength of 2 meters (VHF band, 150 MHz) cannot detect objects that are much smaller than 2 meters and requires an antenna whose size is on the order of 2 meters (an awkward size for use on aircraft). In contrast, a radar with a 10 cm wavelength can detect objects 10 cm in size with a reasonably-sized antenna. In addition a tuneable local oscillator and a mixer for the receiver were essential. These were targeted developments, the former by R W Sutton who developed the NR89 reflex klystron, or "Sutton tube". The latter by H W B Skinner who developed the 'cat's whisker' crystal. At the end of 1939 when the decision was made to develop 10 cm radar, there were no suitable active devices available - no high power magnetron, no reflex klystron, no proven microwave crystal mixer, and no TR cell. By mid-1941, Type 271, the first Naval S-band radar, was in operational use. The cavity magnetron was perhaps the single most important invention in the history of radar. In the Tizard Mission during September 1940, it was given free to the U.S., along with other inventions, such as jet technology, in exchange for American R&D and production facilities; the British urgently needed to produce the magnetron in large quantities. Edward George Bowen was attached to the mission as the RDF lead. This led to the creation of the Radiation Laboratory (Rad Lab) based at MIT to further develop the device and usage. Half of the radars deployed during World War II were designed at the Rad Lab, including over 100 different systems costing US$1.5 billion. When the cavity magnetron was first developed, its use in microwave RDF sets was held up because the duplexers for VHF were destroyed by the new higher-powered transmitter. This problem was solved in early 1941 by the transmit-receive (T-R) switch developed at the Clarendon Laboratory of Oxford University, allowing a pulse transmitter and receiver to share the same antenna without affecting the receiver. The combination of magnetron, T-R switch, small antenna and high resolution allowed small, powerful radars to be installed in aircraft. Maritime patrol aircraft could detect objects as small as submarine periscopes, allowing aircraft to track and