This rare and important Lemania was specially commissioned for crewmen of a Royal Navy nuclear submarine. Unusually for a military watch, this chronograph was specified to have no luminous paint at all. This is so that there can be no chance of errant radiation readings aboard. This non-luminous arrangement, coupled with a bright white dial, afforded the watch a unique model number, which you can see engraved on the case-back, replacing the previous 'Fleet Air Arm' number which has been correctly struck out. 
The watch was manufactured around 1964, and accepted into military service in 1970, according to the primary records shared with us by one of Greenwhich Observatory's Technology Officers of the day.
The watch is a single-pusher chronograph, powered by a beautiful nickel-finish Lemania calibre 2220. The pusher and winding crown are guarded against knocks and damage by the solid steel 'asymmetric' case body.
In ten years, this is only the 6th asymmetric Lemania chronograph we've had, and is our only nuclear submarine model 3312. This is an exceptionally rare watch.