When they captured the large Japanese submarines with the sea plane launching silo ...
they said that when they went down below to inspect the sub that the head just had two holes in the floor like some bars in Japan use to have
(at least that's what I heard)
I-400 Submarine's compartment designed for storing Aichi M6A Seiran seaplanes
The I-400 subs were the largest ever built until the Ethan Allen-class of nuclear subs in 1961
Look at these two subs ... all they ate was rice anyway lol