This was NATO, but the HQ was under US command. One doesn't want to say too much, but it wasn't the hardest place to enter.
Or leave.
Immediately after 11 September 2001, the Turkish guards were removed and replaced by Germans. No reason was given, but there was a feeling on base that Turkey was slightly too non-Christian to be left in charge of perimeter security. I'll never know the real reason.
More than once I left my ID hanging in my appartment and didn't realise until I was at my desk, well inside the wire.
Because I was "The Ukranian guy with a bicycle", nobody checked my pass.
(I wasn't Ukranian at all, but it said UK on my pass and they refused on that basis to believe I was British... )