Waltham Military Timer

This is a Waltham 16 size, 22 jewel, military timer.  It features a black 24 hour dial, sweep seconds, and an open face base metal case.

This is a "hacking" movement, meaning that the watch completely stops in setting mode so as to allow setting to the second.  In this image, the movement is in setting mode and a little spring of steel is touching the balance wheel.  It at the upper right visible near the balance cock.  This stops the balance wheel, and thus the watch.   In winding mode, that spring is moved out of the way and the balance starts.

The black gear on the back is sitting on the 4th wheel.  The 4th wheel is the one that turns one revolution per minute, and this is where, on the other side, the seconds hand would be on a typical pocketwatch (the location of that sub-dial for seconds is not a matter of style, but of mechanics).  This watch has a sweep seconds hand, mounted in the middle.  The black gear drives a pinion on a shaft that passes inside the center wheel arbor, through the watch,, to carry the sweep seconds hand over on the dial side.