an Entity references as follows:
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. APS-4 operated in the X band at 3 cm, compared to the 10 cm S band used by most radars of the era. 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.