Before the development of radar, Navy ships could track other ships or aircraft only by using optical techniques, sound ranging, or primitive radio direction finding. New methods of detection and ranging were necessary. In the autumn of 1922, NRL made the first detection of a moving ship by radio waves and, as a result, discovered the radar principle. Eight years after the initial discovery of the radar principle, NRL scientists noted that the reflections of radio waves from an airplane could also be detected.

The U.S. battleship New York (BB-34)

In 1939, the battleship New York (BB-34) receives the United States' first radar, the XAF, developed by NRL.

From 1930 to 1940, NRL explored the use of radio for detection and ranging, and in 1935 the Committee on Naval Appropriations of the U.S. House of Representatives allocated $100,000 to NRL for the development of radar. This led to NRL's invention and development of the first U.S. radar, the XAF (installed on the battleship USS New York in 1939), and led eventually to its commercial production form, the CXAM. By the time of Japan's attack on Pearl Harbor, 20 radar units were in operation on selected vessels. These radars contributed to the victories of the U.S. Navy in the battles of the Coral Sea, Midway, and Guadalcanal.