C.1939 Grana ATP Official Ordance Military Watch. 
 
The Ministry of Defence only officially ordered 133,000 from various Swiss Manufacturers in 1939, known affectionately as Tommy Watches these predated the famous Dirty `Dozen by a number of years and were used in the heaviest fighting in WW2. 
After the war those that hadn't been lost or destroyed the MOD tried to destroy, however not all were and that makes these watches very collectable now. 
This watch is actually in very good condition for its age and possible wartime experience showing some  signs of wear.
The Army Trade Pattern Mark and Pheon (ATP) is clearly engraved on the back.
Inside the case is a 15 Jewel Swiss Movement 
 
Cosmetically Overall this is in Good Condition and running well