The design was outlined by the US department of defence for general issued military watches.
Benrus and Hamilton both produced watches from the 60s to the 90s based on the design
The modern Khaki and the khakis that went before take their design from these issued watches. The modern ones tend to be a little larger then the issued watches.
Got'cha.
As Sinnlover said above various specs for US military watches were issued and both Benrus and Hamilton made similar versions.
I'm not an expert on US military watches, but from reading into the history of them, MIL-W-3818B was the spec issued in 1962 which is what the Benrus DTU-2A/P was made to meet. Other companies (not including Hamilton) also tendered but only the Benrus was considered to meet the spec. MIL-W-46374 was the updated spec issued in 1964, and the A version was released in 1968 with Hamilton producing metal cased versions.
The 1960's Mil-Spec case size was 34mm which is what Benrus produced after beating Bulova to win the contract in 1962....
Or a modern 39mm version if the style is more important than historical accuracy
NEW SAN MARTIN EXPLORER 36 First Look & Quick Comparison With SMITHS EVEREST!
https://m.youtube.com/watch?v=FiRlDmy617M
I don't remember seeing this before even tho it is a couple of years old.
Costume jewellery. Ouch!!!