In June 1975 Seiko launched a watch that looked like nothing else and solved problems nobody else had solved: the 6159-7010, the first professional diver with a titanium case, rated to 600 meters, wrapped in the protective shroud that earned the whole family its Tuna nickname. Engineer Ikuo Tokunaga's design generated more than twenty patents for the case alone.
Collectors call it the Grandfather Tuna because every shrouded Seiko professional since inherits from it, through the quartz Golden Tuna of 1978 and onward to the present catalog. As the founding document of a line still in production, it is the rare vintage reference whose descendants you can still buy new, which keeps its story alive and its parts ecosystem honest.
The engineering file. Shroud condition is the tell on a Tuna: originals age in a particular way, and a shroud that sits proud, shows the wrong texture, or looks newer than the case has usually been swapped. The professional Tunas were used as tools; honest wear is the expected condition, not a defect.
Production windows and specifications compiled from documented collector references and period catalogs, cross-checked across independent sources; manufacturer records for this era are approximate by Seiko's own account.