For any reason. The tanker must have been on the water.

Full or empty, doesn't matter.

Intentional demolition or scuttling counts but it can't have been planned ahead and intentional.

Sinking counts as destroyed.

Accidentally crashing and being abandoned and sinking counts even if it's pilot error

Intentional planned launch, evac, then sinking wouldn't.

Piracy followed by the pirates planning to sink it and then doing so would count.