IJNS Yamato.

Just a quick question on something that has been bugging me, the Yamato has rear mounted catapults, below these in the hull there are symmetrical openings. Does anyone know what they were for? Rather big for torpedo units and I cannot find out from web searches.

I did find a thread here for a build going back to 2011 but it seems not to have been completed, shame, it was a cracking build.