Raptor1,
The Narwhal is not a stock submarine. It was added by Ducimus (Trigger Maru) and FooFighter (the skin).
There is a way to have 2 deck guns, but you have to get into some files to set up the crew manning manually. I don't remember which files though, sorry.
edit: Look at Fincun's post on this thread.
http://www.subsim.com/radioroom/show...t=missing+crew