To confirm what Brag has claimed, yesterday evening I bagged a Revenge-class BB with a torpedo hit to its bow.
What happened was that I was on my way back to Wilhemshaven with only 2 torpedoes left. I received an intel report about a slow convoy & since it wasn't far away I decided to intercept it, and sink the largest ships I could with my remaining torpedos.
Well, the largest ship I saw was the BB, so I aimed one eel under the forwardmost turret, and the last one under the smoke stack - I was hoping to hit the ammo storage and engine room respectively.
Unfortunately an escort got too close & started pinging. As a result the convoy started weaving which screwed up the targeting solution. The first eel missed just forward of the BB, but the second hit at the bow, roughly at the area where the ship's anchors are stowed.
The hit started a small fire, and the bow became lower and lower in the water until it submerged. At the end the ship went down almost vertically, in less than half an hour game time!
BTW this is my first ever capital ship victim in SH3 after numerous patrols, so as you can imagine I'm rather pleased with myself.