As used by navigators on the B-17 Flying Fortress and B-24 Liberator aircraft during WWII, this is a 1942-dated example of the Hamilton U.S Army Air Force GCT Navigation watch, type AN 5740. The GCT or AN 5740/AN 5740-1 pocket watches were used for navigation purposes by all branches of the US Military prior to, during, and after WWII.  The three main manufacturers of this watch type were The Hamilton Watch Co., The Elgin National Watch Co. and the Waltham Watch Co. During World War II, Hamilton, Waltham, & Elgin produced a variety of time pieces to support the war effort. In fact, all of Hamilton's production was dedicated to defence purposes.  One of their war-related watches was a pocket watch with a central sweep second hand.  The movement was based on the 21 jewel, 16 size movement. However, an extra jewel was added to support the second hand pinion, so the movement got 22 jewels.  Thus, the AN 5740 was created, and became known as a "Navigator's Watch," as it was used by aviators to aid in navigation during wartime bombing missions over German-occupied Europe. You will see that it has a 24 hour dial, so it takes a full day for the hour hand to make a full rotation. Therefore, 12:00 noon on a 24 hour dial is positioned where 06:00 would be on a 12-hour dial. The minute hand still makes it around the dial in one hour, so the ratio of the minute hand to the hour hand is modified using a different minute wheel and hour wheel ratio. Given its age and purpose, the watch is in overall good condition, with only slight wear to its nickel finish on the hanging loop.  Its bezel exhibits various marks and scratches, so would benefit from a light polish to bring it up to its best.