The computer shown in use for the army's transmitter was actually an 80s home computer, manufactured by Commodore. It's either the C64 or VC20. They shared an almost identical casing design in the early 80s. The branding of the device used in the movie was taped over.
Pamela Hallisey Hiss's debut.
Original title: Secrets of the Phantom Caverns.
The film is dated 1983 in the credits.