Sea Dog (シードッグ) also known as Mariner’s Run is a cancelled RPG / submarine simulation / Shoot ‘em up game planned to be published for NES / Famicom by Vic Tokai. A couple of screenshots were found in old gaming magazines by japanes fans and shared on Twitter, while some details were published online in a japanese website:
“Although gameplay is not clear on screenshots, it seems Sea Dog was going to be a vertical-scrolling submarine shoot ‘em up with some RPG elements. Between deep-sea exploration and combats you would be able to rise to the sea level and stop at nearby ports. You probably could repair your damaged submarine and buy new weapons.”
We could imagine Sea Dog somehow similar to cult-classic Metal Max, but with real-time underwater shoot ‘em up combat instead than post-apocalypse turn-based combat around desert cities. By looking at the few screenshots available we can assume you would have been able to freely explore the ocean underwater, while fighting enemy submarines and hunting down bosses, then reaching nearby islands to help NPCs and upgrade your submarine. The title of the game was probably inspired by the USS Sea Dog, a Balao-class submarine in the United States Navy.