AN 5740 military pocket watches were issued to aircraft (primarily bomber) navigators in all service branches during WWII and into the early post war period. Watches meeting the specification were manufactured by Elgin, Waltham, and Hamilton. Unusually for a pocket watch, they have a central second hand and a hacking mechanism, as well as a 24 hour dial. They were typically mounted in special cases, meant to protect the watch from the effects of vibration, temperature and altitude, and were generally set to Greewich Mean Time (hence the G.C.T. on the dial). This Hamilton example, despite its age, still tells time very accurately.