I stand corrected. The early wristwatch era isn't my strong suit. Once you get past the Cartier Santos, I skip to the later stuff.I beg to politely disagree it is the original chronologically speaking (1909), check-out this well written article:
History of the Pilot Watch Part II - Zenith Montre d'Aéronef Type 20 - Monochrome Watches
The point being that you will see similar styles from other brands contemporary with Zenith as well, so it's an established "style" -- like Fliegers or field watches.