It is an early wrist watch sometimes called a trench watch in collecting circles. Gents wrist watches were first marketed as an essential part of an officers equipment during the First World War.
Previous to WW1 most people wore pocket watches if they could afford a watch.
These were not "issued" like the latter ATP/WWWs but were a private purchase from jewellers.
The only way to tell if it may have been used in the trenches is via family testimony.