The AN/APS-4, originally known as ASH (air-surface, model H) is an early military air-to-air and air-to-surface radar used by American and British warplanes during World War II.

This allowed the antenna to be greatly reduced in size and the unit as a whole to fit into a single streamlined fairing that could be mounted to many aircraft.

In Fleet Air Arm and RAF service it was known as ASV Mark IX and equipped a number of aircraft including the Fairey Firefly, Fairey Barracuda, de Havilland Mosquito and a small number of Grumman Avengers.

[2] The antenna and transmitter-receiver were typically housed externally below one wing, in a fiberglass shape that was similar to a Mk 17 500-pound (230 kg) bomb.

In intercept mode, the beam executes a four-line scan, with 6° between lines, to cover a vertical plane of 24°.