This is a vintage replica of Vietnam-era Benrus MIL-W-46374 disposable military watch made by Korean company Saeki. It features a dark olive drab colored one-piece plastic case with fixed lugs. 18 jewels manual wind movement is supplied by Japanese watch company Citizen. Black dial has H3 and radioactive tri-foil symbol to denote use of tritium for luminescent markers on the dial and hands, which has faded. These type of replica military watches were usually sold at shops just outside military base during the 80s and were popular among Korean soldiers because they were cheap and looked like the real thing.

Caseback is marked with pseudo military numbers and codes:

SAEKI WATCH PURPOSE
SKA 073-82-002
JIANT
JUN 1981
DISPOSE-RED-WASTE
WATER PROPE. MADE IN KOREA

As you can see, there are misspelling and other errors, showing that maker had absolutely no idea what the military markings found on an authentic military issue wristwatch meant. It's actually quite amusing and cute.