Although it isn't connected to any landmark achievements in exploration.
One watch that has fascinated me for a while now is the Brook & Son Submarine.
Although I'm still surprised at how little know it is, considering how advanced it was for its age.
Here we have a watch that was not only "Waterproof" a decade before the Oyster case but also antimagnetic 20 years before the Tissot claim.

(not my watches sadly, sill on the hunt for one of my own)

David Boettcher has done some wonderful research on it and his blog is well worth a read.
http://www.vintagewatchstraps.com/blogsubmarine.php