This is a Glycine Airman from Vietnam-era. It's an early version that has lacks the Glycine crown symbol on the dial and has the date in red numbers. The crown at 8 o'clock is for releasing and tightening the 24 hour bezel so that it would not rotate accidently by casual bumps and such. Very useful feature that should be incorporated into all GMT/24 hour watches.

What is truly unique about these early Glycine Airman is that when you pull out the crown, a tiny hair spring pops up at the 24 hour position which allows the second hand to come to a complete stop at that position for precise time setting (i.e. hack). Swiss made 25 jewels automatic movement is signed Glycine and is housed within a beautiful snap back case. If you're a pilot or frequent traveller, this is the perfect watch to keep track of multiple timezones. It's so perfect, tracking secondary timezone is an instant process. In fact, many US pilots during the height of Vietnam war used this watch instead of their issued watch.