velopment of the Armstrong radar. In 1946, Sylvania received a subcontract from Republic Aviation under Army Air Force Project MX-773 to develop a guidance system for a 500- 1500 mile surface-to-surface missile. Although celestial and inertial naviga- tion were possibilities, it was decided that a radio-controlled system using FM ranging would be the most easily realied. Accurate high-frequency (HF) ranging requires that the receiver extract the ground wave propagation and ignore the potentially strong skywave mul- tipath, as well as ambient noise and jamming. The MX-773 subcontract spec- ifications called for satisfactory discrimination against interferences of the following types: 1. Skywave, identical in modulation to the ground wave guidance signal but forty times greater in amplitude and delayed 100-250 us. Other guidance signals identical in modulation, but fifteen times greater in amplitude and differing in arrival time by 50-2000 us. 3. Unmodulated, pulse, or noise-modulated inteference up to twenty times the guidance signal in amplitude. These time resolution and interference rejection requirements eventually motivated the use of wide-band modulation techniques. Norman harvey, the leader in this development effort, states: The MX-773 project started out in a strictly study phase, with no special link- age to the FM radar project. It was the specification of 0.5 mile accuracy at 1500 miles that initially gave us the greatest concern. At the time, DECCA (England) was operating a pure cw, cycle-matching navigation system that attracted our interest because it promised that kind of accuracy under ideal conditions. Bob Bowie, John Wilmarth of Republic Aviation, and I went to England in the spring of 1946 to attend the Provisional International Conference on Air Organization (PICAO), to look particularly at DECCA, but also to see if there were other systems that might be adapted to meet our requirements. Not long after that, the idea of combining a DECCA-type cycle matching sys- tem (for accuracy) with FM modu