The Seiko 6139 series automatic chronograph - like the full-serviced near new-old stock 1978 Seiko 6139-7101 "Bobby Deerfield" automatic chronograph here, on its original stainless-steel "fishbone" bracelet - serve as an excellent example of Seiko placement of their movements into multiple highly unique cases, leading to a plethora of out of the ordinary shapes and sizes.
 
The 6139 - a historical movement in its own right - was the world's first automatic chronograph, beating out the likes of Heuer's Calibre 11 and Zenith/Movado’s El Primero movement.  Back in the late 1960's, Heuer and Zenith had taken hold of the entire sports watch industry by racing to become the first to produce an automatic chronograph.  It has been widely debated who won, but in the background of this skirmish, Seiko quietly created their own at the same time, beating the Swiss at their own game – the Seiko Ref. 6139. 
 
During the early months of 1969, Seiko put the final touches on its revolutionary 6139 chronograph - in fact, the Japanese company first began putting the 6139 in automatic chronographs as early as January of the same year.
 
Seiko published its first advertisement for their new automatic 6139 chronograph in February 1969, easily beating the Swiss - however, the company was concentrating on the release of the world's first quartz watch, the Astron, which would completely disrupt the watch world as it was known at the time (again, much to the chagrin of the Swiss watch industry, we're certain). We possess 6139 dials dating back to November 1968, indicating Seiko beat all other rivals to produce the world's first automatic chronograph.  Period.
 
The watch world recognized this recently, with an early model Seiko 6139 - January 1969, well before the Swiss - garnering nearly $20k at auction.
 
The 6139 was the first chronograph to have a vertical clutch, a feature considered by many to be one of the hallmarks of a superior automatic chronograph movement.  The 6139 also features an automatic column wheel timing control, vertical coupling mechanism, and is an integrated chronograph – the first in the world – which means the entire 6139 movement was designed and built to be a chronograph, vice being an automatic movement with a mere timing module added.
 
With this movement, Seiko set the standard, which was followed by the Swiss watch industries 20 years later.  The same movement configuration was adopted by Rolex when it made its own in-house movement for the Daytona in 2000, 30 years after Seiko released the caliber 6139 and 6138.
 
Of note, Al Pacino wore one of these 6139s in the 1977 American romantic drama "Bobby Deerfield" - directed by Sydney Pollack and starring Pacino and Marthe Keller, it was based on Erich Maria Remarque's 1961 novel "Heaven Has No Favorites," about a famous American race car driver (Pacino) on the European circuit who falls in love with an enigmatic Swiss woman who is terminally ill.
 
This 6139 comes on its original Seiko-signed "fishbone" stainless-steel bracelet, and with nylon strap, springbar tool, and rugged travel case.