This is a Japanese wargame of submarine warfare in the Atlantic during World War 2. 1 rulebook, 2 data sheets, 2 hexmaps, 2 log pads, 4 countersheets, 2 playaids, 2 dice 1 hex = 93m, 1 inning = 1 minute This game uses call-marker system that Tsukuda first invented in Task-force series. Escort ship cannot see submarines. And submarine cannot see escort because they go undersea. But, this game doesn't use double-blind. Instead, this use call-marker.