Using the deck gun

Hello all. I'm having an issue using the deck gun. I am running Sobers Mega Mod and really enjoying the 'new game' after an absence of a couple of years!!!
However, I cannot for the life of me get to the large deck gun in front of the conning tower.
If I press F5 or F6 I can get the crew to man the guns behind the tower (and I can operate them too) but no crew goes to the front gun and I cannot find a way to man it myself. HELP!

Also, one other question, how do I start the Trevally Kiel canal script? I have it running with the other mods, I just do not know how to start it within the game?

Thanks in advance, your help is always appreciated.

CookieGuy