If your being realistic there were only 3 Yamato class ships ever built. Two were Battleships and one was converted to an aircraft carrier. All were sunk during the war. Fully loaded your only going to get around 72,000 long tons out of each in real life but the game does not model the tonnage to real life so you get even less.
In the game I have never used less than 6 fish in sinking one and 99% of the time it takes 8 or more in game. I have used as many as 12 to do it.
A Gato carries 24 fish. In any case good luck finding all three in a single patrol. It was never done in real life.
There is a fluke with a certain mod that after a certain date you can find the Yamato sailing out of the Bungo every day at around 1500. I got three that way on one patrol. It tool every fish I had and I got around 180,000 tonnes.
Unless your running the one hit wonder fish your never going to be able to sink 300,000 tonnes in one patrol without a refit.
