The Vintage Wrist Watch Company has dated this piece to the 1910s.
The Mark V watch was manufactured for the Royal Flying Corps for use in cockpits. There were four known manufacturers of the watch, namely Zenith, Omega, Doxa and Electa... there were other manufacturers but they preferred to remain anonymous.

The watch came in three forms, the 30 hour non-luminous version such as the watch we have here, the luminous edition for night time pilots to monitor fuel consumption and navigate in the dark and then the eight day version which was ideal for longer flights.

This particular watch has a stem-winding movement which is working nicely. The movement is signed with the Zenith name and the serial number 2,320,260 dates it back to 1919.
The watch itself measures 57mm diameter excluding the winding stem and the loop.
This is a later case, possibly adapted for civilian use.
The later acrylic lens is in good condition.
The dial has the CB code, used by Zenith. The hands appear to have been repainted at some stage, and the infill has been removed.
The watch will be sent in a new presentation box.
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The Vintage Wrist Watch Company has dated this piece to the 1910s.
Specialists in antique and vintage wrist watches and pocket watches
You can view the stock and full dealer information on the The Vintage Wrist Watch Company Profile Page