This is a special watch, as it's one of the first wrist watches transposed from a pocket watch ! 
 
Designed for use by soldiers in the trenches who could not dig a pocket watch out of their uniforms when they needed to check the time. Made as the Ingersoll Midget Pocket a nickel case with an open front, made in 1911-12  the movement here is dated to 1912,  converted to a wrist watch by the addition of D-Loops on the 12 and 6 positions.
 
An interesting fact, these watches were frequently handed out to tank crews when they started to arrive on the Somme on the 15th September 1916, The life expectancy of tankers was expected to be a short one so they were issued with these watches as they were relatively inexpensive. The fact that this watch is still around and working is impressive !