I recently went heavily into debt. Sacking towns is a key part of my strategy. But then, Spain wasn't at war with anyone and after that it was at war with Holland, whose towns are unassailable (I can sometimes do English towns and always French ones - I wonder if this varies from game to game rather than being an insult to the froggies). I was 2.7 million gold down at one point.

I had had the bright idea to keep lotsa sabres for when this happens, but I ran out of sabres, so attacking towns by land wasn't an option. Alas, I couldn't attack by sea, either. My ships appear and they can flee, but otherwise they don't respond to commands.

I eventually clawed my way back to solvency, but this is a problem again because of the mission where you have to attack a military convoy at a certain town, after which you have to attack the town to complete the mission and it isn't possible to just flee. Who can help?

How do you make them flee, do they respond to sailing out of the map?
If the wind is seaward, you'll have to beat to come closer to the shore (sailing diagonal towards the shore).

Stupid question, but you don't have the game paused by any chance? (Spacebar or Pause key)

Just for reference, here are the controls for sea battles:
DURING SEA BATTLES
1-0 Key select ship 1-10
Shift Key fire
+ Key increase sail surface
- Key reduce sail surface
Insert Key attack
Home Key escape
Delete Key board
End Key select all
Pause or Space Bar stop time
F10 Key select massive cannonballs
F12 Key select grape-shot
F11 Key select chain-shot

I don't mind you asking if I have the game paused. I don't, but I expect the problem is something silly like that.

I flee by clicking on the "flee" button at the top right of the screen. This gets ships moving and allows me to attack the port, although I'd rather not have to do it.

I think I have to attack with one ship at a time, because I can't control more than that. I'd like to see how damaged my ship is - they sink so very easily. How do I do that?

Attacking by sea takes ages and usually, I'm unsuccessful.

EDIT: I used to be able to defeat towns with the loss of only one battleship, back when battleships were like gold dust. Then, a ship could make three passes of the gun emplacements, but now, it only manages one. Advice on tactics would be appreciated.