There exist numerous vintage Seiko divers popular with "Seikoholics" collectors, but none more so than the venerable 6309 series - like this iconic 1977 Seiko 6309-7040 automatic diver here - with its long history of use in Cold War-era (and beyond) military operations.  
 
The 6309 was quite popular with the U.S. military, akin to the Seiko model it replaced, the 6105 - its (much more expensive) forefather - and quickly became the staple of the working diver and the USMIL (both regular forces and Special Forces).  In fact, U.S. Navy Naval Special Warfare units favored Seiko divers (in particular the 6309) - for an example of U.S. Navy SEAL Team Six forces being issued a Seiko 6309, Watches of Espionage (WoE) related the story behind legendary Navy SEAL Rudy Boesch and his Seiko 6309 diver in "SEAL Team Six and A U.S. Navy-Issued Seiko Turtle." 
 
Per WoE, “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."
 
"Boesch enlisted in the Navy at 17 years old and had a 45-year career in Naval Special Warfare, making him the longest serving SEAL at the time.  He was originally an Underwater Demolition Team (UDT) Frogman prior to joining the newly formed Navy SEALs in 1962."
 
"Boesch earned a Bronze Star for his actions during two combat deployments in Vietnam with SEAL Team 2.  After Vietnam, Boesch returned to Little Creek, VA with SEAL Team 2 and it was there that he was issued this Seiko in 1979…Boesch [remains] a legendary figure in the Naval Special Warfare community, and years later became well-known to the general public due to his participation in the reality show “Survivor.”
 
With the creation of Special Operations Command (SOCOM) in 1987, its first Commander in Chief General James Lindsay selected BMCM Boesch to serve as SOCOM's first Senior Enlisted Advisor.  Before his retirement, Boesch was designated the "Chief SEAL" (a.k.a. "Bullfrog"), a title identifying the longest-serving SEAL still on active duty.  Upon his retirement from the Navy on August 1, 1990, as a Command Master Chief Petty Officer, he was awarded the Defense Superior Service Medial.
 
Per former SEAL T.L. Bosiljevac, in his history of SEAL operations in Vietnam, Boesch symbolized much of what the SEAL teams represent, "There are a lot of colorful personalities among the teams, but even considering the best of those, Rudy Boesch is a legend.  Everybody knows Rudy, and you can bet that Rudy knows everyone in return ... [including] some of the Navy's top brass."
 
The 6309 series of diving watches was the third generation of Seiko’s recreational/professional divers. The 6309 line replaced the 6105 in 1976 and was produced until 1988, when Seiko replaced it with the 7002 diver.  6309’s - like this one here - were a successful effort by Seiko 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 frontman Mic Jagger and legendary actor Ed Harris (who also wore a Seiko 6139 "Cevert" in the "Apollo 13" film, but that's another story) personally owned one?  Moves like Jagger, indeed...
 
This Seiko 6309 diver comes on a leather-backed cavas strap, and with nylon strap, rugged travel case, and springbar tool.