Elgin Grade 463

The grade 463 is a 3/0 size, 7 jewel movement.

This one was made about 1918.  It placed in a military-style wrist watch case, with the protective grill at the front.

Wrist watches, being considered feminine, were not commonly worn by men at this time.  The early use of watches in the military is what began to change this.

As an aside, new military tactics emerged in this era as well - tactics involving coordinated, timed, actions by ordinary troops.