I made a purchase on the "Bay" of 5 Hamilton 921's and 945's movements last week, which the cases were scrapped for the gold. I had this dial just waiting for a special movement and think it fits the style of this watch pretty well!
The Movement was manufactured in 1941 and was in very clean condition, only needing a light service.
I'd be very wary of these "trench watches" - there are so many of them out there. They may well be 1910s - or 1920s - or even 1930s. Unless they're silver and hallmarked - or unless they have a WW1 Ministry of War marking (crow's foot or "pheon") on the back, I never touch them.
There's a vogue for things military, and sellers try and cash in on this. Same with "railroad" watches - many are simply not RR grade.