Made by Hamilton Switzerland (now part of the Swatch Group), not the original US company; these watches were standard issue to all three British armed forces, the only difference between the watches issued is the case back engraving, which shows that this one was an Army watch. Its issue date is 1973, so it is likely to have seen action in the Falklands conflict of 1982.
The case is an unusual one piece case in a tonneau shape, the movement is removed through the glass opening at the front, after the split winding stem is removed. The movement itself is a Hamilton cal 649 (actually an ETA 2750) with 17 jewels, with incabloc shock protection & a hacking seconds facility.
The rear of the case has full British military markings, including the issue number, the marks are:
the MOD broad arrow
The watch measures 32.5mm Diam, 41mm lug to lug and is 10mm high; it takes an 18mm strap and has fixed strap bars, the watch runs well and keeps time, and it has been serviced.