I think my biggest boom was from a Kongo. Hit one with an under the keel shot from my aft tube that went off right below the front battery. Huge boom that set off a huge secondaries like mad, up and down the ship. Was exploding for a good 20-30 seconds.

Sunk like a rock after that.
*EDIT* And to clarify, the under-the-keel shot wasn't intentional. I meant to shoot it deep, but not under the keel. Either I set the depth too low, or it ran deep. Either way, worked out for me.