Re: Hamilton 21 numbers
While browsing through "MANUAL FOR REPAIR AND HANDLING OF HAMILTON SHIP CHRONOMETER WITH PARTS CATALOG" Contract N8ss-2270 Bureau of Ships Navy Department October 1948 (M. Trauring reprint), I found some notes on the allotment of the Hamilton ship chronometers to Navy ships:
"Capital ships of the U.S. Navy (battleships, carriers, cruisers) are allotted two or more of these chronometers. Thus, the navigator can compare readings for more accurate determination of time and longitude. For safety, the chronometers are located in different stations aboard ship, according to the discretion of the ship's Commanding Officer."
"Fighting ships other than capital ships (destroyers through submarines) and seagoing ships (such as supply ships, tenders and hospital ships) are allotted one or more chronometers and one or more gimbal chronometer watches. Usage is similar to that on capital ships. For the exact navigating timepiece allowance on a particular type of vessel, reference should be made to the latest timepiece allowance list."
This is all pretty far from my main area of interest (railroad watches) so I can't add anything to what is in the manual. Just keep in mind that all that was applicable over sixty years ago; I don't even know if any ships carry chronometers these days! Maybe someone with more contemporary knowledge can add something.
By the way, the manual states that "Serial numbers as assigned by the U.S. Navy are engraved on each chronometer dial and the barrel bridge." I believe those are the numbers preceded by the N in a circle. The other numbers, with the 2E (not posted), 3E and 4E prefixes, as shown in the records posted by Tom (post #8 above) are clearly the factory serial numbers.
I hope this is of some help.
Larry Treiman