In my previous career, what happened is that I was able to detonate a magnetic underneath its fuel tank or ammo bunker (not sure which one) and the ship would be considered destroyed. Unfortunately I haven't been able to get the magnetic into the same area this time around
On the other hand, I did sink an Ocean Liner and a Large Tanker in Dunkirk, and then a Modern Tanker in Calais on the same patrol. The thing with those ships is that they didn't blow up either, they just sank regularly, so that's why I'm so bumbed out about the Hood.