The Seiko 6138 automatic chronograph - like this 1971 Seiko 6138-0017 “Yachtman” JDM automatic chronograph here - has a well-known cult status, hence the nickname “UFO” (although advertised by Seiko as the “Yachtman Chronograph”) due to its flying saucer-esque case design.
 
The UFO features an innovative and simple construction, such as a unique lug-less case, very indicative of the 1970s in which it was made, its pushers (held in place by the movement’s spacer ring) and crown are well proportioned for the case size. The oddly numbered 6138 was the successor to the 6139 - the world’s first automatic chronograph - after its introduction in 1969, and the 6138 followed closely behind and was likewise produced by Seiko until 1979.
 
The 6138 SpeedTimer variant of this watch was sold only in Japan, and was not widely known outside of the country - unless, of course, one considers a comical McDonald's attempt to seemingly exploit child bereavement in a 1990s commercial in the UK.  The fast-food behemoth was forced to withdraw the ad following widespread complaints - but it did feature the Seiko 6138 UFO.
 
The main differences between the 6138 and 6139? The 6138 offers hand-winding and featured two chronograph registers versus the sole one on the 6139. The Seiko 6138 contains subdial registers measuring minutes and hours, whereas the 6139 only measured minutes.
 
The 6138s, due to larger movement size, also tend to be at least several mm's larger in size, in particular the Seiko 6138 UFO here. Indeed, most 6138 are unusually sizable for the 1970s era, with the UFO here measuring 44mm (46mm w/crown) in width.
 
The 6138 was technically at least equal to its Swiss counterparts, as it featured a fully integrated chronograph vice stacked modules. There were two versions of the 6138, with the first, the 6138A, introduced in 1970 with 21 jewels. The 6138B was introduced subsequent and featured 23 jewels; both versions featured a column wheel that regulated chrono functions, and a vertical clutch mechanism for engagement – hallmarks of a serious chronograph movement.
 
Seiko's 6138A/B automatic movement is designed as a two-register chronograph, counting up to 30 minutes on one subdial and another 12 hours on the second dial. All 6138 movements feature a quick-set day/date indicator and can be manually wound (unlike the 6139 model), relatively unique for Seiko chronographs of this era.
 
The UFO’s black dial is contrasted with silver subdials and orange/red highlights on the central chronometer hand, dial and the external tachymeter bezel, and its fully integrated chronograph render it truly a landmark design, easily pitting it against the Zenith El Primero.
 
With the 6138 movement, Seiko - as usual - set the standard followed by the Swiss watch industry 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 its 6139 and 6138 calibres.
 
This Seiko UFO comes on a quite loyal homage to the original presidential-style bracelet this watch was sold on - it also comes with a nylon strap, spring bar tool, and rugged travel case.