A “Living Letter” tape recording as we knew them during the Vietnam War was originally called A “Letter on a Record”.
This brainchild was originally fostered by the USO some time in World War II.
By the Vietnam era they had segued from vinyl disks to magnetic audio tapes.
I purchased what was commonly referred to as a tape deck (AKAI X-1800SD) for the express purpose of both recording and playing voice messages to and from my family.
We had 50′ audio tapes on 3″ reels in small pre-packaged mailers available from the base PX (Post Exchange).
I received this WOKY Radio92 air check and enclosed letter mid-tour:
The air check was recorded over Friday, June 20 and Saturday, June 21st, 1969.
I can be found at 38:46 in recording.