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.