After screwing up a convoy approach a couple of nights ago, where I mag-shot 3 Black Swans but they did not sink - they take a hit and run back into convoy formation after getting damaged - it was dark so I blew ballast and shot to the surface, manned the guns, and was able to take down the wounded Black Swan from about 3400 m. I hit them several times to sink and they never hit me back.
Guess I'm better with the gun in GWX than I thought.
Don't think I'd try this during the day though.
Steve