In 1968, Seiko received a letter from a professional diver in Kure, Japan – a port city in the Hiroshima prefecture – explaining that the current diveoffered by the brand simply weren’t good enough. On prolonged saturation dives, the 62MAS and other early Seiko divers stood no chance against underwater pressure. Kaizen, a Japanese word for “improvement,” has been a business-school buzzword, and back in the day, it was more a sense of reasoning that Japanese people and businesses lived by, inherently or explicitly. The spirit of Kaizen is more specifically “improvement in all facets, whenever possible.” The Kure-based diver’s letter provided an open door for Seiko’s engineers to spring through. After seven years and filing for 20 patents, the “Tuna” diver emerged in 1975. More than a clever nickname, the tuna reference is not to the fish but rather to the lack of lugs and circular bezel shroud that mimic the shape of canned tuna. This “Golden Tuna” is the second generation in the product line of 600m capable divers and dates to 1981. The black and gold tones as well as the large but extremely wearable and surprisingly comfortable shape are the model’s calling cards.