Answers:

4: Watford City, ND. The hilltop where the FAA joint-use long-range radar operates today was earlier the location of the Alexander (ND) gap-filler annex. The Alexander GFA was originally an operating location of Dickinson AFS, ND, and later Minot AFS, ND, after Dickinson AFS closed. [Recall from Quiz #1 that Gibbsboro AFS, NJ, a blue-suit site now JSS site, also started its radar existence as a gap-filler annex.]