Will Fly- During WW2,both Waltham and Hamilton watches were purchased for the military, for use where accurate timing was required.
Ord = Ordinance Department; they purchased, tested and supplied many items used by the Army. All sorts of technical equipment may bear their inscription, and possibly a serial number.

I have a 17j Hamilton, inscribed "Bureau of Ships, U. S. Navy comparing watch, 12457-1943." The last is the supply catalogue number and date it was tested.

Another I have is a wristwatch, used by the Canadian Air Force. I haven't opened it, but some were Omegas.

Especially desirable are Hamilton 21j watches used in the military; one can easily sell for $1000. Wish I had one!