allowing a single antenna to perform both functions had not yet been perfected. Similar microwave gun-laying systems were being developed in Canada (the GL3C) and in America (eventually designated SCR-584). Although about 400 of the GL3B sets were manufactured, it was the American version that was most numerous in the defense of London during the V-1 attacks. Royal Navy The Experimental Department of His Majesty's Signal School (HMSS) had been present at early demonstrations of the work conducted at Orfordness and Bawdsey Manor. Located at Portsmouth in Hampshire, the Experimental Department had an independent capability for developing wireless valves (vacuum tubes), and had provided the tubes used by Bowden in the transmitter at Orford Ness. With excellent research facilities of its own, the Admiralty-based its RDF development at the HMSS. This remained in Portsmouth until 1942, when it was moved inland to safer locations at Witley and Haslemere in Surrey. These two operations became the Admiralty Signal Establishment (ASE). A few representative radars are described. Note that the type numbers are not sequential by date. Surface Warning/Gun Control The Royal Navy's first successful RDF was the Type 79Y Surface Warning, tested at sea in early 1938. John D. S. Rawlinson was the project director. This 43-MHz (7-m), 70-kW set used fixed transmitting and receiving antennas and had a range of 30 to 50 miles, depending on the antenna heights. By 1940, this became the Type 281, increased in frequency to 85 MHz (3.5 m) and power to between 350 and 1,000 kW, depending on the pulse width. With steerable antennas, it was also used for Gun Control. This was first used in combat in March 1941 with considerable success. Type 281B used a common transmitting and receiving antenna. The Type 281, including the B-version, was the most battle-tested metric system of the Royal Navy throughout the war. Air Search/Gunnery Director In 1938, John F. Coales began the development of 600-MHz (50-cm) equipment. The higher frequency allowed narrower beams (needed for air search) and antennas more suitable for shipboard use. The first 50-cm set was Type 282. With 25-kW output and a pair of Yagi antennas incorporating lobe switching, it was trialed in June 1939. This set detected low-flying aircraft at 2.5 miles and ships at 5 miles. In early 1940, 200 sets were manufactured. To use the Type 282 as a rangefinder for the main armament, an antenna with a