Original Item: Only One Available. This is a great example of the Elgin-Hamilton developed USAAF AN5741-1 8 Day clock, designed for Airships. These really are a marvel of Watchmaking design, featuring FIVE dials, the main 24 hour clock face, and 4 sub dials. These include a dial for the clocks seconds, a 32 day CIVIL DATE dial, a 12 hour dial for ELAPSED TIME, and a dial for 60 minutes or hours. Additionally, the clock also has a chronograph function, which is what some of the dials are for. All together this is an amazingly complicated and beautiful piece that shows the amazing engineering the U.S. was once capable of.

The controls consist of a button for the chronograph in the upper right corner, which starts, stops, and resets it. In the lower left corner is the mainspring winding knob, which pulls out to adjust the time. There also is a button on top of this, but we do not know what the function is. There is also a SET DATE button that advances the CIVIL DATE dial one day for every push.

The back of the bakelite housing still has the complete manufacturers information:

AN 5741-1
MFRS. PART NO. H-37500
CONTRACT NOs 96322
MFRS. SER. NO. 000697
HAMILTON WATCH CO.

The watch is in very good condition, with the expected wear from age and use. The clock does seem to function, though the chronograph function does have issues. When used, it seems to seize the movement when it hits 15 seconds, stopping the clock as well, so it definitely is not fully serviceable.

NOTE: This clock is sold as is, and we cannot guarantee that it will run when received. It is being sold for collectors purposes only.

More on the Elgin-Hamilton AN5741-1 Clock:
War has a way of making things hard to get, and when it came to getting precision time instruments from Switzerland, one can imagine the priority the United States placed on that. As a result, the U.S. Government set about creating military specifications for timepieces. One of these specifications called for the development and manufacture of the Hamilton/Elgin 37500 aircraft clock, also known as the AN-5741-1.

Before the American entry into WWII, planes were equipped with the LeCoultre Elapsed Time clock named the “Chronoflite.” Beautiful in its own right, this clock was quickly made obsolete because of a lack of spare parts, and movements. As war efforts ramped up, both Hamilton and Elgin factories devoted all their production and development efforts to fill the timepiece void. Some of the most legendary American timepieces came out of this era, including the Hamilton Model 21, Model 22, G.C.T., A-11, and the 37500.

Both Hamilton and Elgin made the 37500s in 1944-1945. The companies were jointly awarded a contract to develop and provide the military with a very unusual and uniquely complicated piece. The book Military Timepieces by Marvin Whitney gives a great insight into the conception and development of this iconic aviation piece.

Upon both companies’ inspection of the Chronoflite, they spotted four main design defects that they fixed with the 37500:

1) They added a second mainspring.

2) They changed the winding system.

3) They fixed a setting problem with the Chronoflite that caused teeth to wear rapidly.

4) They redesigned the civil date mechanism so that the pin that changes the date would not break or bend when being set counterclockwise.

The last mechanism was patented by Hamilton engineer Francis Meyer and granted on October 10th, 1944, as patent #2,360,305

Also, unlike many clocks of the time, they used a fluorescent luminescence paint that is activated under UV light as an alternative to the more common (and dangerous) radium. Containing over 400 parts (417 to be exact) this clock combines several interesting functions, and the scale of it makes it a perfect size to fully be able to appreciate these complications.

First, it is a 24-hour clock, meaning the hour hand circles only once per day. This is a very common aviation theme, as found in other iconic pieces like the Glycine Airman. The clock was also equipped with a one-button chronograph with a 60-minute counter, an elapsed flight timer (essentially a chronograph with hours and minutes but an entirely separate mechanism from the chronograph) on the bottom sub-dial, and a civil date. The date is also a quickset activated by a button located slightly above the winding crown. All together this is an amazingly complicated and beautiful piece that shows the amazing horological engineering the U.S. was once capable of.