No. Airfields can’t be destroyed. Four hits will damage two enemy airfields, if there are two on the island. Excess hits are just wasted.
Artillery used in the Sea attack
How do you score a hit on a artillery unit that is participating in the sea battle or is it a free shot? Since it is a land unit do we wait till the land battle to decide what is destroyed?
It’s a free shot, just as ships bombarding islands are free shots. Artillery can only be hit during the Attack Land Units step.