Marker Beacon Receiver R-122A/ARN-12 is a lightweight airborne marker beacon receiver utilizing a superheterodyne type circuit with a crystal controlled oscillator. It is designed to give aural and visual indications when flying over any army marker beacon transmitter at altitudes between 10 and 4,000 feet, and over CAA marker beacon transmitters at altitudes between 100 and 35,000 feet. Reception is on the standard marker beacon channel of 75 MHz. The equipment responds to a 75 MHz. signal which is modulated by 400 , 1,300 and 3,000 cycles. The receiving set is designed for operation from the aircraft 24 volt dc. system.

A filter is required for selection of indication of 400, 1,300 and 3,000 cycle modulation. This is provided in a separate unit which may be installed or omitted depending upon the mission of the aircraft.   This equipment replaces Marker Beacon Receivers RC-193, RC-39, and RC-43.

 Army Supply Program requirements as of 1 February 1945 were 11,860 sets for the calendar year 1945, and 23,599 sets for 1946.