To unman the deck gun, order your sub to surface, they'll jump right off.
The default game only has uselessly small rudder changes (arrow keys left or right) or drastic ones (Shift+ Arrow keys left or right). There are some mods, like DarkWraith's 3 Dials mod, that add back in the compass rose and Rudder display though.
You can also simply look in whatever direction you want to go and use the +/= key (next to backspace) to Heading to View.
Glad you're enjoying the game, it's quite fun once you get past the negative comments!
