Offensive airports for defensive wings

while setting up defense wings, and choosing from a list, it only allows me to set them up at offensive airports. Is this correct?

addendum: same for setting up defensive land forces, and choosing from a list, only allows offensive military base.

It's correct.

Then why have a defensive military airport or base?

You're supposed to be able to move things around on a bigger map, but I keep getting an error message when I go there.

On the small map I can't even see it - going to try and play with the visibility settings.

If you have to have a defensive base to have defensive troops, but they are delivered to an offensive base, maybe some automation is in order, like having your supply outfits ferry em over?