There is no multi weapon fire. It was on the list from the very beginning (and it would look cool), but the balance was such that as you can win with a single gun, multiple weapons would have made it too easy. I also had to work the AI to stop them from firing all their weapons at once, which absolutely annihilated the player during development. And I never quite worked out how to handle the UX of selecting what weapon(s) to fire. Solvable problems though. I think I could tune weapons easily enough.
I get people's frustrations with firing off screen and the low reward, but that (and having to use your base to take some hits etc) was all completely intentional. It's about surviving by the skin of your teeth, not smashing through at the end with all the goodies. Making players question: do I fix things now, I try another round and make more money.
I appreciate the feedback, positive and negative.