The Seiko Prospex HBC005J1 is the premium model in Seiko's second wave of 145th Anniversary Prospex limited editions — the 1965 Heritage Diver in Seiko Blue, limited to 4,000 pieces worldwide. Built on the 1965 Heritage platform that traces its design DNA directly to the 62MAS — Japan's first diver's watch, produced in 1965 — the HBC005J1 takes the iconic compact 40mm case and applies the 145th Anniversary Seiko Blue treatment: a blue aluminium unidirectional rotating bezel, a blue seconds hand, and a silver-white dial that creates the clean, cool, formally modern aesthetic that defines the entire 145th Anniversary series. At 4,000 pieces, it is more exclusive than the 9,999-piece HBB001K1, and more accessible than the 2,500-piece HAB004J1 Astron.

The specification is where the HBC005J1 separates itself decisively from the HBB001K1 sibling. The 6R55 calibre delivers +25/-15 seconds per day accuracy and a 72-hour power reserve — a full three-day reserve versus the HBB001K1's 41 hours. The curved sapphire crystal with anti-reflective coating on the inner surface replaces the Hardlex of the larger sibling with premium optical clarity and scratch resistance. And the water resistance rating is Diver's 300M — 50% deeper than the HBB001K1's 200M, and one of the highest ratings available in any 40mm steel dive watch in this price range. The three-fold clasp with secure lock, push-button release, and solid and slide adjuster completes a full professional diver's specification in the 1965 Heritage's compact and historically grounded case.