Stand By, Ready
A friend wondered why the Defenders have no Core Squadron card. I guess they just cross-attach them to everything else--though in the show they seem to be the chief close-in AA defense artillery for the SDF-1.
I suspect it is because a 4 Defender Air Defence Squadron Core Unit would only be 40 pts. (+10 for Airburst rounds)
Which would make them a cheaper way of being able to added special and support to other units, than is currently available.