Patek Philippe

Hi fellow connaisseurs, have encountered a (for me) rather strange watch which has been referred to as " WW1 Trench Watch"... Is said to be pre 1940s, with a 14k gold face. Poor pics, I know (bad lighting, no better available), but does anyone know anythi...  

... that's why I'm asking... ;-) Dial and movement both read "Patek Philippe" and strangely have a "1918" added, not only on the dial but also on the movement... Never heard of this or seen it before. Did PP do business with the military forces...? Thanks... 

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