The actual historical Maru-yu had several problems diving. It was an experimental ship (made by the Army, which didn't like working with the Navy much) and on its first few test-runs, it failed to dive. Then, it managed to dive, but couldn't surface afterwards. -_-U
Kiso was apocryphally in port at the time of some of this, (although historians say it was probably actually Ooi...) and her crew commented on what a strange-looking submarine she was. (At least, if you count the whole production line of Maru-yus as just being "Maru-Yu"...) Because of this, Maru-yu and Kiso are typically shown as old buddies in KC comics after Maru-yu "proves herself".
Usually that is called sinking, or we would call every downed ship "expediently converted underwater vessels".
Maintaining depth above seafloor is generally precluded from sinking, though.
Ah... okay.Please observe!Ah...Even Maruyu can dive properly, you know!Idea: Yuuji
Artist: Kouji
Kancolle 2-koma Theatre, Part 32Can you actually go underwater?