Deck gun quandry

[UnderseaLcpl]

Hey all,
Another noob question as I near the end of my first campaign; I'm skippering a lovely Balao and just saw the option to buy fore and aft 5/25 deck guns. I couldn't resist the temptation of having 2 5" guns : )
However, it seems impossible to man the aft gun. I searched the forum but I only found a discussion where the Narwhal mod was brought up and the consensus seemed to be that it was the only sub with 2 guns.
I'm running stock 1.4 for now and I removed the deck gun crew from their slots before pulling into port.
Are there any mods or fixes that can enable my aft gun or do I just get stuck with a 25 caliber paperweight?

Thanks in advance!