Seiko first entered the dive watch market in the 1960s, after a request from a local diver to build something that could hold up during deep sea dives using diving capsule and saturation techniques. His complaint was that upon reaching greater depths, most watches would malfunction and become damaged. The answer to this request was for Seiko to establish a development team to design a timepiece that could perform reliably under the extreme conditions of deep sea diving, and they did so magnificently.

One of the most notable characteristics of the Marine Master SBDX023 is the case. The mono block case is just 2 pieces, the stainless steel case and the bezel. There is no case back. The case is polished using the Zaratsu Polishing Technique, which is mirror blade polishing technique performed at the Grand Seiko manufacturing facility. The case is then treated with Seiko’s DiaShield coating to prevent scratches during wear. The crystal is sapphire and the movement is a Caliber 8L35B movement, which is based off of Grand Seiko’s 9S55 movement. The dial is black with gold colored hands which are filled with Seiko’s own Lumibrite luminescence composition, as are the number plots and the first 20 markers on the bezel.

Included with this Seiko Prospex Marine Master Professional 300M Ref SBDX023 are the original outer and inner boxes, owners manual, guarantee certificate, all original hang tags, the stainless steel Seiko bracelet and an additional Seiko black rubber strap with stainless steel Seiko buckle.