making a default deckgun

[sfc]

I've been trying to figure out how to set the default deckgun on the different classes of subs in SH4, so many times the game sets it at a stern gun and I prefer the bow gun. any ideas guys?
also have been looking at how to get the twin 40s early in the war, even with the later towers installed early I can't get the upgrade.
I know that alot of what I have done to the game is not real-its still fun.