The use of a pulse technique to detect aircraft and ships was proposed by NRL's Leo Young in 1933. His colleague, Robert M. Page, made important advances over the next few years in the area of transmitters and receivers. He eventually developed the highly important duplexer, which permitted an antenna to be used for both transmitting and receiving. Combined with the duplexer, the pulse technique did away with the separate receiving and transmitting antennas that early radar developers had used.
In 1940, NRL developed submarine radar. This radar enabled a submarine to rise to periscope depth and search for hostile aircraft before surfacing. Aircraft could be detected by the radar out to a range of 20 miles. At that time, this was considered adequate to allow the submarine to submerge before becoming vulnerable to the aircraft's weapons. This radar became popular with submarine skippers during World War II; units were installed in submarines as quickly as they became available-more than 400 were produced. The Laboratory later perfected a directional radar antenna for use with the Western Electric Radar System. It was effective enough to be used as a fire-control instrument, allowing several enemy ships to be torpedoed without the submarine being seen.
To provide a polar-coordinate map-like display of targets, NRL originated the radar plan-position indicator (PPI)-the well-known radar scope with the round face and the sweeping hand-between 1939 and 1940. The PPI is now universally used by military and commercial interests around the world for the display of radar information for such functions as air and surface detection, navigation, air traffic control, air intercept, and object identification.