How do I destroy the Battleships?

In the mission in Northfork where you need to destroy the battleships in the naval station, I don't know what I need to do

I can survive the swarms of VTs but I don't know what to do about the two ships in the distance.

I think shooting at them with the tank gun won't do anything, so there must be something else that needs to be done.

What do I need to do to complete this mission?

Thanks

Does this mean you didn't beat the level either?

Bummer...

I think you have to hit the guns themselves, but they seem to stay intact after getting hit by AP, then unfortunatetly I get blown apart by the ships AP

I figured out how to get past this level.

I destroyed serveral VTs then went under the crane on the right side of the map and that seemed to trigger the mission clear status

Then I spent the remaining time destroying VTs and the mission was completed succesfully instead of failing when the time ran out.

I still don't know if you can destroy the battleships but at least I got past the level