Repairing a World War II Navy Chronometer - The Iconic Hamilton Model 21

Published at : 12 Dec 2025

This is the most expensive broken watch (or clock?) I've purchased on eBay. It was sold to me at a "discounted" price of about $1,600 due to issues that I'll uncover and repair in this video. It's hard to call this a "deal" at that price, but in the end it was worth it.

World War II created a dire chronometer shortage for the United States. Before the war, most chronometers for American military and civilian customers were imported from Europe so we had that unfortunate supply chain dependency on that part of the world. In 1939, anticipating war, the U.S. Naval Observatory sought American watch manufacturers to mass-produce chronometers. Hamilton and Elgin participated, but only Hamilton met the Navy’s accuracy standards. Early 1942, Hamilton’s prototypes were selected after passing with a +/-1.55-second daily error rate. During the war, Hamilton produced approx 8,900 chronometers for the Navy, 1,500 for merchant ships, and 500 for the Army. In contrast to other movements of the time, Hamilton incorporated the detent escapement and the helical, corrosion resistant elinvar balance spring to maximize the accuracy it could produce.

These chronometers were specialized timekeepers for determining longitude at sea. A chronometer set to a known time standard like Greenwich mean time, allows sailors to determine their longitude by comparing it to local time. Since one hour of time difference equals 15 degrees of longitude, the time gap between the chronometer and local time reveals the ship’s longitude.

#restoration
#watchrepair
#clock
#chronometer
#military

Contact info: cspinnerwatchrepair@gmail.com

Many of my tools I use are affordable. If you're interested in getting started with watch repair and would like to use what I use, I've included some links below. I earn a small commission from Amazon if purchases are made using these links.

Useful Texts:
I am pleased to be part of Chronoglide's affiliate program. If you are not familiar with the company, Chronoglide is a professional watchmaker in the Netherlands. They have an excellent YouTube channel by the same name. I'm excited to share their team has written a book called "Watchmaking Explained" - Everything you need to know as a watchmaker, but no one is telling you. A practical guide for all watchmakers and enthusiasts! Their book is designed to be interactive, loaded with QR codes linking to additional videos and content. https://www.chronoglide.nl/boek/aff/3/

Other texts:
Watch Repairer's Manual: https://amzn.to/3knrwdG
Watchmaker's Lathe: https://amzn.to/3D02WGb

Tools:
Micrometer: https://amzn.to/3vPPuUy
Micrometer Stand: https://amzn.to/3vPPuUy
Microscope: https://amzn.to/3ZrQ3Pn
Movement Holder (pocket watches): https://amzn.to/3H9JBUv
Movement Holder (wrist watches): https://amzn.to/3JeG2iv
Ceramic Tipped Tweezers: https://amzn.to/3QP1qMH
Finger cots: https://amzn.to/3CXbXzJ
Micrometer: https://amzn.to/3QNGN3C and Stand: https://amzn.to/3iIyF86
Rodico: https://amzn.to/3kr5RBb
Tweezers: https://amzn.to/3GNFEVi
10X Loupe: https://amzn.to/3iLfome
Levers: https://amzn.to/3XB4RZG
Demagnetizer: https://amzn.to/3ZINUhS
Budget Screwdrivers: https://amzn.to/3Xr7gqo
Better Screwdrivers: https://amzn.to/3SZRGkY

Cleaning:
Mesh Baskets: https://amzn.to/3ITqikE
Ultrasonic: https://amzn.to/3wcO7wg
Mason Jars: https://amzn.to/3WkUfgB
Cleaning Solution: https://amzn.to/3XwQ16I
Rinsing Solution: https://amzn.to/3wdgAlA
Cleaning Brushes: https://amzn.to/3QPnSp8

Lubrication:
Oilers: https://amzn.to/3Xi8LXR
DX Grease: https://amzn.to/3ZO0kVU
Moebius 941: https://amzn.to/3Hf6g2X
Moebius 9010: https://amzn.to/3CVGM7Y
Moebius D5: https://amzn.to/3ITqikE

Buffing and Polishing:
PolyWatch: https://amzn.to/3XlVTja
Polishing Compound: https://amzn.to/3QQ1r33
Bench Buffer Polisher: https://amzn.to/3OlcW2E

Chapters:
0:00 Introduction
1:40 Begin Disassembly
20:29 Cleaning
23:54 Fusee Cone Repair
26:34 Begin Reassembly
29:31 Making a Tool
33:08 Continue Reassembly
42:40 Escape Wheel Repair
43:30 Continue Reassembly
45:23 Detent Escapement Demo
46:48 It's Alive!
47:22 Brass Bowl Restoration
49:45 Gimbal Repair and Final Steps