Thanks Olivoil;
Since I am (though becoming less so , it seems) primarily a military watch collector, this Longines stop second from 1938 did indeed perk my interest when I first happened upon her. Ziggy includes the 12.68z stop in A Concise Guide to Military Timepieces, suggesting their use by the US Navy, if I recall correctly. This one was sent to Baume in the UK, possibly still military use.
Though it's small- 33mm- it's one of my favorite Longines. Sadly, it's now off at the watchmaker for some pivot post adjustment.