Original U.S. Vietnam War Hand Held AN/PRT-4A Radio Transmitter Spanish Military Equipment It is marked with an

It is marked with an inspector stamp

From the data plate visible on the inside of this unit

where it participated in the VIII Corps Brownwood Maneuvers until 13 June 1941

and those integrated with French units were given French M15 Adrian helmets

and is marked on both the top of the barrel and the lock (faint) by the maker:

Original U.S. Vietnam War Hand Held AN/PRT-4A Radio Transmitter Spanish Military Equipment It is marked with anOriginal Items: Only One Available. Introduced in 1965, the PRT 4A is a 2 channel crystal controlled handheld FM transmitter, for use with helmet receivers as part of a set. The A version transmits a 150 Hz tone that opens the squelch on receivers so equipped, such as the VRC 12 series, the PRR 9 (XE 9),and PRC 25 77. Power output is 450mW on Channel 1 and 50 250mW on Channel 2. The radio has an empty skeleton detachable bottom BA 399 U battery