It's about as iconic a "Hamilton" design as it gets. The design harkens back to military designs as far back as the 40's. Hamilton has produced this basic design almost continuously for decades.
I have no idea exactly when they started, but here's one from the Vietnam era..............look familiar?
MILITARY WRIST WATCH, VIETNAM ERA HAMILTON | eBay
Lot's of companies at one time or another produced the classic "militaty" design..................Hamilton is unique in that they have produced it the entire (or most of it) time. Like the Rolex sub this design has become associated with Hamilton.