Hamilton Military Chronograph
"The Hamilton Model 23 Chronograph was used by all branches of the armed forces but predominantly used by the Air Force during WWII and into the 1950's Korean conflict. The Model 23 Chronograph had several uses.
It could be used as a traditional "Ground Speed watch" which would help the Air Force navigators correctly determine the ground speed while in flight. This is important for so many reasons such as properly determining where you are for navigation, safe drop speeds for paratroopers, fuel consumption and obtaining correct speed for bomb drop trajectory.
It could also have been used for artillery drills and on U.S. Naval vessels and submarines or any other circumstance where an accurate timeframe was needed to be measured.
However, the Model 23 was most often used It was also used by the US Army Air Force during WW II in conjunction with the Mark III, Model 5 Octant or Pioneer (BendiX Aviation Corp) A-5 or A-7 sextant for navigational purposes while in flight over water where landmarks were not available.
A sextant or octant was used to measure the "altitude" of a celestial body above a horizontal line of reference. ("Altitude" in this case is a special use of the word describing an angular measure, not a distance in feet above sea level.) A mariner can use the horizon as this line of reference, but when an airplane is flying above the clouds or flying at night, its navigator can't see the horizon. The bubble sextant or octant solves this problem by providing an artificial horizon. It takes its name from an air bubble in a liquid-filled chamber that functions like a carpenter's level, indicating when the sextant or octant is aligned horizontally.
The navigator would look through the eyepiece of his sextant or octant and locate a star. With a drum on the side of the instrument (like a camera's focus ring), he would adjust the angle of a rotatable prism until the star showing in the eyepiece is aligned beside the bubble. The prism and drum are geared to circular scales, marked off in degrees. From these scales he could read the star's "altitude".
But just as importantly as knowing a reference star's "altitude" the navigator had to know the exact time that the reading was taken. To do this, before taking the "altitude" reading, the navigator would start the Model 23 at some specific time, say 12:34:00 GCT. Once he had the star aligned beside the bubble in the sextant or octant, he would depress the pendant and stop the sweep hand and record the time of his observation along with the "altitude" reading from the circular scales. Since it was difficult to take a reading on a bouncing airplane, several reading of the same reference star were taken and averaged. To obtain a "fix" usually required observations of three different stars."
Some more information:
"The HAMILTON MODEL 23 MILITARY CHRONOGRAPH pocket watch was widely used during WWII by navigators as a stopwatch. It is a 19 jewel, 16 size watch adjusted to temperature and 3 positions and was paired with the US Navy Model IV octant, as well as a couple of other sextants. the Model 23 was clipped to the side of the Mark IV octant and a trigger pushed the button on the Model 23 to stop and start the stopwatch. Based on the extremely reliable 992B with Elinvar hairspring and mono-metallic balance, the Model 23 adds a chronograph mechanism making it one of the most complicated watches produced by Hamilton. This base metal Keystone Watch case is very well preserved with only normal wear to case and back. Back is engraved with military marking FSSC NO.-88-W-590 Mfgs. Part No. 37297 Hamilton Watch Co. FSSC 88-W590 is the number of this particular design of watch in the Federal Standard Stock Catalog. The catalog was to avoid having the same item with different numbers in various parts of the US military."
I would like to thank James Kitchen of Austin for providing the watch below for my website:
"The only reason for time is so that everything doesn't happen at once." Albert Einstein