Let's get this out of the way - there's only two watch companies with such strong reputations for making tool watches that can make patina - evidence of a life lived with the purpose that a tool watch was designed for - attractive.
 
Namely, a Swiss company that starts with an "R" and...Seiko.
 
And this is one of those watches - a full-serviced 1981 Seiko 6309-7040 automatic dive watch here - with its long and well-documented history of use in Cold War-era military operations (and beyond).  
 
Crowned by Watches of Espionage (WoE) as "One of history’s most important diving & military watches," the 6309 was popular with the U.S. military (and militaries further afield from the America, as well), akin to the Seiko model it replaced, the 6105 - its much more expensive forefather.  After it's debut, the Seiko 6309 quickly became the staple of the USMIL (both regular forces and Special Forces) and commercial divers everywhere.  U.S. Navy Naval Special Warfare units - aka Navy SEALs - favored Seiko divers, in particular the 6309.
 
Per WoE, "Backed by impressive military history, a utilitarian design format, widespread adoption in our community, and a more attainable price point compared to other icons in the world of undersea timekeeping, the 6309 is among the most important diving and military watches of all time, full stop.  I would even go as far as to say it is the most iconic Watches of Espionage watch of the last five decades, issued to and worn by SEALs, Pararescuemen, Special Forces, and others."
 
"Not limited to official issue, the 6309 was also commonly purchased by military members at the local PX or Navy Exchange.  In past profiles of special operators, which are extensive at this point, the 6309 is easily the most commonly encountered mechanical dive watch in the late 70s and 80s.  When U.S. Navy SEAL Dave Hall shook hands with Scout Sniper legend Gunny Carlos Hathcock after completing sniper school, a Seiko Turtle was on his wrist.  When Jose Gordon was a young Army Ranger assisting the Contras in their fight against communism in Nicaragua in the 1980s, he wore a Seiko 6309."
 
For an example of U.S. Navy SEAL Team Six forces being issued a Seiko 6309, WoE tells the story of legendary Navy SEAL Rudy Boesch and his Seiko 6309 diver in "SEAL Team Six and A U.S. Navy-Issued Seiko Turtle." 
 
“Originally, the Seiko was issued to revered SEAL Rudy Boesch in the late 1970s, and SEAL sniper Kyle Defoor acquired it in 1996 when his father purchased the watch at an auction supporting the UDT-SEAL Association and gave it to him.  Defoor wore the watch in training and operational deployments, including the early years of the war in Afghanistan."
 
The 6309 series of diving watches was the third generation of Seiko’s recreational and professional divers.  The 6309 line replaced the 6105 in 1976 and was produced until 1988, when Seiko replaced it with the 7002 diver.   Seiko 6309’s - like this one here - were a successful effort by the Japanese watch manufacturer to improve the 6105 movement, which allowed for greater lifespan, robustness, and ease of maintenance.
 
The 6309 line was produced in two separate case variations: an earlier cushion case, popularly known as the “turtle” for the appearance of its cushion case, which was produced between 1976-88, and a slimmer case version from 1982-88 (the 6309-729A).  The former featured so-called "Suwa" dials (for the Japan-based Suwa factory mark between the had post and the six o'clock position) from 1976 through at least 1981; following this, the Suwa symbol was removed from the dial - the "non-Suwa dial" - until Seiko ceased production in 1988.
 
Oh - and did we mention both Rolling Stones legendary frontman Mic Jagger and actors Ed Harris (who also wore a Seiko 6139 "Cevert" in the "Apollo 13" film, but that's another story) and John Candy personally owned one?  Harris' appears to be his own 6309, as he has worn it in multiple films throughout the last three decades.  A slew of other actors have worn the same watch throughout the past several decades on various television shows, Erik Estrada in "CHiPS" (1977-1983) and Nicholas Gonzalez in "Blue Ridge" (2024) 
 
Moves like Jagger, indeed...
 
This Seiko 6309 diver comes on a new Seiko DAL1BP rubber dive strap, and with nylon strap, rugged travel case, and springbar tool.