Like your sounds, nice work! explosion5 and fire2 don't sound like much, but the rest are good and make the game nicer, thanks
You may be right concerning fire2. I avoided using some very specific firing sound, since the file is used to represent all kinds of long range fire, from land based artillery of all sizes, to naval guns, so I preferred some kind of distant rumble sound, for effect.
As for explosion5, this is the same sound. Explosions 4 and 5 are there as alternatives. The original sound set contains explosions 1, 2 and 3, so I think those will never be played without renaming. Maybe I'm wrong though. Maybe the code checks for numbered alternatives, but I wasn't able to notice it while testing.