A genuine U.S. Vietnam War era C-2329B / GRA-39 control radio set. The GRA-39 (C-2328 & C-2329) is used in conjunction with a radio receiver-transmitter or a local battery switchboard to expand the interfacing capability of the radio or switchboard. When connected with a radio, the GRA-39 enables the operator to transmit and receive voice frequency communications through the radio for a distance of up to two miles (3.3 kilometers) from the radio. When connected with a switchboard, the GRA-39 is used 10 accomplish net radio interface (NRI), by which voice communication is established between a field telephone (switchboard subscriber) and a radio. Was made by Sentinel Electronics Inc USA and has a 1967 dated contract number. Excellent condition, retains the majority of the original paint, nice and clean inside, with a clean battery compartment.