Harold Adelbert Zahl (August 24, 1904 – March 11, 1973) was an American physicist who had a 35-year career with the U.S. Army Signal Corps Laboratories, where he served as the director of research at Fort Monmouth and made major contributions to radar development.

His first assignment was to provide assistance in coastal defense by installing undersea cables that picked up sounds from ships and submarines to determine their exact location.

Zahl recalled that this cable-laying operation was initially misinterpreted by the locals as an attempt to impede rum runners, which led to many of the cables being cut overnight.

[7] As a research physicist for the Signal Corps, Zahl worked on numerous projects involving acoustics, infrared, electron tubes, and radar.

In 1940, he invented the GA-4 Transmitter-Receiver Tube, a duplexer made it possible for the Army and Air Corps’ early-warning radars to transmit and receive signals from the same antenna.

[12] At the close of World War II, Zahl left active duty as a lieutenant colonel in 1946 and became a civilian employee at the Signal Corps Engineering Laboratories, where he promoted the continuation of scientific collaborations between universities, industry, and the military.

[1] In 1948, Zahl was named the director of research at Fort Monmouth's Camp Evans (later called the Army Electronics Command Laboratories).

[3][13] During his tenure, Zahl was involved in the Space Race against the Soviet Union and spent much of his time tracking the path of Sputnik I when it launched in 1957.

[14] Over the course of his 35-year career at the Signal Corps Laboratories, he authored 50 technical publications in the fields of molecular and atomic physics, x-rays, acoustics, and thermodynamics.