It's one engine on each side which is destroyed, but it looks like I've had it and will be loading a previous save

.
I hope I saved it when I started heading back to base, otherwise I'll loose all the tonnage I sank.
Thanks for the help anyway.
EDIT: Just read the post you linked to rrmelend. Seems like I'm a victim of the game design flaw/bug. Ah well, I'll just learn to avoid getting shot at then!