Assuming the USAF work to U.K. Rules (which are very similar to Fighting Edge) the minimum height would be 5000'. Standard airmanship dictates that you remain clear of active airfields, built up areas, cloud, controlled airspace and danger areas (unless you're booked into it).
It would seem odd to cr@p on your own doorstep in this regard since they are local and probably know better.
More importantly, were they any good?
BV