The Japanese have the best conventional subs in the world, but snorkeling while recharging batteries is revolutionary?
The Kriegsmarine might want to discuss that with the Japanese MSDF.
OK, that’s funny right there!
I think what’s revolutionary is the quick charging of the LI batteries, such that you’re at the surface / snorkeling with the diesels running for a much shorter period than with longer-charging-cycle lead-acid batteries.