Silver cased Hamilton 4992B navigation Master Watch

This is a fairly scarce solid silver cased Hamiton 4992B military watch.
The 4992B movement was a development of the superb 992B railroad watch. In this guise an additional jewel was fitted to accomodate the centre seconds sweep hand, the watch was converted to pendant set, the final gearing adjusted to provide one revolution of the hour hand in 24 hours, and a "Hacking" feature was added.
The hacking feature allows for precise time setting and for synchronisation with other timepieces. When the crown is pulled to time set position the watch stops, when depressed to normal winding position the watch immediately restarts. So by allowing the seconds hand to advance to the 24 (Top) pull out the crown the watch will stop, advance the main hands to the next full minute and when that time is reached depress the crown and the watch will restart. So the time is now set to the precise second. These watches proved to be so accurate and reliable  that other watches within the same unit were synchronised to them hence the "Navigation Master Watch" title.
The movement in this watch is in absolute tip top condition running strong and proving to be an accurate time keeper.
The 0.800 silver case is in very nice condition, and unusually for a silver cased version this one has the military engravings on the rear cover. Both front and rear covers remove and replace readily, and close down square and tight.
The black 24 hour dial in super condition with all of the printing clear and sharp, and with a nice set of white painted hands to indicate the time. This is a 24 hour dial with the 12 where you might normally expext to find the 6 so reading the time can take a bit of thought as the hour hand takes 24 hours to complete one revolution.
Abeautiful example of this highly collectable watch in the scarce silver case.