An uncertain I-500 successor to the I-400

If the I-400 was a dead-end idea, would the I-500 have been better?

No firm judgment is possible because the supposed I-500 is not identified confidently; a long-range submarine without the aircraft installation is only a tentative recollection.

The supposed I-500 successor cannot be identified confidently. Alex Clarke recalls a proposed follow-on or conversion retaining the I-400's range while removing its aircraft-carrying capability, but explicitly allows that he may be mistaken. Another participant can find only a fictional I-500 reference, and a possible amphibious concept adds further uncertainty. The exchange therefore does not establish that the design existed or that it would have improved on the I-400. The suggested advantage remains conditional on a long-range submarine without the aviation installation being the intended referent.