When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The back of the watch states as follows:AN5740MFR\'S Part No. 4992BSerial No. AF-42-16697Contract No. W535 ac-28072Hamilton Watch Co.
I have no other information other than I purchased it at an sale in Fort Collins, Colorado in 2011.
All of the following information was obtained off the internet with the information off the back of the watch provided, please verify the information if you wish as to determine for yourself it accuracy
The watch is a Hamilton 4992B Navigation Master Watch (often called a \"G.C.T. watch\"). During WWII, the Hamilton Watch Co. completely halted civilian production to manufacture these ultra-precise instruments, which were used by US Army Air Corps and Navy bomber navigators to calculate longitude and plot flight paths across oceans.
A breakdown of exactly what each marking on your case back represents reveals its history:1. AN 5740 (Army-Navy Specification Number)The AN 5740 code indicates a standardized military design. The \"AN\" stands for Army-Navy, meaning this exact watch design was approved and ordered jointly by both branches of the US military for aviation use.2. MFR\'S PART NO. 4992B (The Movement Designation)This refers to Hamilton\'s internal manufacturing part number. The 4992B is a legendary, high-grade watch movement featuring:
- 22 Jewels: Hamilton adapted their famous \"992B\" railroad watch by adding a 22nd jewel to support a sweeping center seconds hand.
- The \"Hacking\" Feature: When you pull the crown out to set the time, the second hand completely stops (hacks). This allowed an entire squadron of pilots to synchronize their watches to the exact second before a mission.
- Adjusted to 6 Positions: It was factory-calibrated to maintain hyper-accuracy regardless of the temperature or the angle it was held.
3. SERIAL NO. 42-16697 (The Military Tracking Number)This is the military\'s accounting and contract inventory number, not Hamilton\'s factory number.
- The \"42\" prefix means that the funding or contract for this specific batch of watches was allocated in the fiscal year 1942.
- The \"16697\" is the sequential military production number for that year\'s order.
The Contract No. W535ac-28072 engraving is the definitive proof that your watch was built specifically for the U.S. Army Air Forces (USAAF)A breakdown of exactly what each segment of your contract number means reveals its history:1. The W Prefix (War Department)The W signifies that the contract originated directly from the United States War Department, which managed the nation\'s military forces and massive industrial production scale-up during World War II.2. The 535 Code (The Air Corps Supply Depot)The number 535 represents the specific government procurement bureau code. It tracks back directly to the primary buying depot for military aviation gear, based out of the legendary Wright Field in Dayton, Ohio (the birthplace of aviation research and procurement for the Army Air Forces).3. The ac Designation (Air Corps)The lowercase ac stands explicitly for Air Corps. This identifies your watch as an item intended for flight crews, confirming that it was destined for aircraft cockpits rather than ground troops (which used different branch codes like ord for Ordnance). [1]4. The 28072 Sequence (The Master Order)The 28072 is the specific block order number under the fiscal year 1942 budget allocation. Hamilton manufactured tens of thousands of movements under this massive, multi-year production contract to supply B-17, B-24, and B-29 bomber crews as the United States rapidly scaled up its air campaigns in both Europe and the Pacific.What to Look for on the Dial and InsideIf you look at the front and inside of the watch, you will likely see its other defining features:
- A 24-Hour Dial: Unlike standard 12-hour watches, the hour hand on a 4992B only goes around the dial once per day. The dial is numbered from 1 to 24 because military aviation operated on a 24-hour clock.
- G.C.T. Markings: The dial usually features the letters G.C.T., which stands for Greenwich Civil Time (now known as GMT or UTC). Navigators kept this watch set strictly to London/Greenwich time to calculate their position using celestial navigation tables.
- The black dial confirms that your Hamilton 4992B was originally issued to the U.S. Army Air Forces (USAAF) or U.S. Navy Bureau of Aeronautics, specifically for nighttime and low-light cockpit use.
