Seiko's 6139 automatic chronograph - a historical movement in its own right, like this full-serviced late 1970 Seiko 6139-6011 "Deep Blue" transitional automatic chronograph here - was one of the first automatic chronograph movements created, and rightly counts itself within the ranks of the world's first automatic chronographs, with Heuer's Calibre 11 and Zenith/Movado’s El Primero movements.
 
Seiko did their homework when they designed these deep blue dials, and pictures do not do these justice - these dials are amazing to behold in person, and this dial here is no different.
 
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 calibre. 
 
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  October 1968, indicating Seiko beat all other rivals to produce the world's first automatic chronograph.  Period.
 
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 (**cough cough** the Calibre 11).
 
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.  This particular Seiko 6139, the 601x variant, represents yet another variant of Seiko's famed 6139 automatic chronograph line.
 
The transitional 6139 inhabited the a time period from 1970 through 1971 - in early 1969, the 6139 was sold with a "waterproof" signed case and dial, 6139A automatic movement, two-piece chronograph second hand, and a "notch" in the case over the crown.  However, Seiko - to comply with a U.S. law deadline of January 1972 - changed the 6139 to feature a case and dial marked with "waterresist" nomenclature, single piece chronograph second hand, and a 6139B automatic movement (among other changes, depending on the 6139 model).
 
In between these two Seiko 6139 models was the transitional model, like this 6139 here, which features a mix of parts from the two - this one here features the later 6139 chronograph hands and the 6139A automatic movement and 6011 caseback of an early 6139.
 
This Seiko 6139 Deep Blue comes on a likely Uncle Straps stainless-steel "railroad" bracelet, and with nylon strap, rugged travel case, and springbar tool.