A very rare Omega trench watch from the First World War. 
 Large 42 mm watch with no protruding parts.  The last photo shows a regular size 35mm watch for comparison (not included in the lot).
Cupronickel silver case with hanging lugs in art deco style.  
Mineral glass.  
The mechanism is high-quality gold-plated with 15 stones.  
The enamel dial has small cracks (visible through a magnifying glass) and a chip in the enamel between the numbers 11 and 12 (restored, hidden under the bezel and not noticeable).  
Approximate year of manufacture: 1915. 
I will answer all questions.