Haraka,
Literally - a Triumph Spitfire just fitted under the Guard Room road barrier with an inch or so to spare.
You were lucky!
There was a similar barrier at Akrotiri circa 62-4, before the area to the Tower and Electronics Centre.
I was manning it one night when the OO came along in his Triumph Spitfire, insisting that I didn't lift the boom, so he could see if he could get under.
He did. At walking pace.
On his return journey, he didn't stop and went though at about 30 to 40 MPH, the car must have been bouncing a bit, as he didn't quite make it!
I bet his insurance claim made interesting reading.