Seiko's dive-watch heritage traces to 1965, when the brand released the ref. 6217-8000, Japan's first domestically-produced 150m dive watch. Designed for the Japanese Antarctic Research Expedition, the watch carried Cal. 6217 automatic and pioneered the Seiko approach to professional tool watches: domestic engineering, in-house movements, value-for-specification pricing. Through the 1970s and 80s Seiko produced the iconic ref. 6105 ("Captain Willard", worn by Martin Sheen in Apocalypse Now), the ref. 6309, the SBBN001 "Tuna" (1975, the first 600m saturation-diver from Seiko), and various professional references for the Japan Maritime Self-Defence Force.
The Prospex name (short for Professional Specifications) was formally introduced in 1989 in Japan and rolled out internationally as Seiko's umbrella professional sport-watch family in 2014. The line consolidated the previously separate Marinemaster, Land Master, Sky chronograph, and Tuna sub-lines under a single Prospex banner, with consistent specifications: 200m water resistance minimum on dive references, 4R / 6R-series automatic or quartz solar movements, and the X-shape Prospex logo on the dial.
The current Prospex catalogue includes the SLA series (high-end reissues of vintage Seikos with Cal. 8L35 chronometer movements; SLA017 / SLA037 / SLA063 reissue the 1965 6217), the SPB series (mid-range 6R-movement automatic dive references including the popular SPB143 / SPB147 / SPB153), the SRP "Turtle" series (cushion-case homage to the 1976 ref. 6309), the SRPB "Samurai", the SBDX "Marinemaster", the SBBN "Tuna" 600m / 1000m monoblock saturation divers, and the Speedtimer chronograph revival (SRQ035, SSC813 reissues of the 1969 first-Japanese-automatic-chronograph).
Movement architecture spans quartz solar (Cal. V157, V175 with 10-month reserve), the 4R36 automatic (entry-level), the 6R35 / 6R55 automatic with 70-hour power reserve (SPB-tier mid-range), and the 8L35 chronometer-grade (no day-date, hand-assembled, used in SLA flagships). Retail spans approximately USD 350 (Solar Tuna SNE573) to USD 6,500 (SLA047 vintage reissue) to USD 15,000+ (SLA063 limited). The Prospex remains Seiko's biggest-volume serious-tool-watch family and a long-standing collector favourite for value-per-specification.
