[Phoenix-D]

Behind, really. All I'm seeing from that link is a midget underwater aircraft carrier. An impressive technical achievement, but..very limited ammo and only three planes. They'd be utterly annhiliated in an attack, and even if they all made it back the carrier didn't have much ammo. (they could only attack once with torpedos, for example).

The smallest atomic bomb developed during the war weighed 4000 kg; the only way the Sen Toku could have attacked with nukes is if Japan somehow made a bomb 20% that size. Wikipedia lists its maximum depth as 100m, less than US subs of the time.