AA Guns could fire on Non-Combat as well, if you were playing “Always Active AA Guns.” A condition that shipped in the CD Rom. Personally, I liked the option at times, meant bombers flying to S. Europe for SBR got shot at by the W. Europe AA Gun, the S. Europe AA Gun and the W. Europe AA Gun again. :)
But that was the only time I know of where they fired in NCM.
As for defending fighters, they may land on any Aircraft Carrier, coast or island in that Sea Zone if their original carrier was destroyed. They cannot land on a carrier in another sea zone.