HTB, the Hunter most assuredly
was supersonic. Neville Duke's booms were a feature of Farnborough Air Shows of the early 1950s. No doubt the PNs would have stated 'the aircraft is supersonic in a shallow dive', without actually defining 'shallow'....
On 11 Aug 1976 at RAF Brawdy, I saw the highest and lowest speeds I'd ever seen whilst airborne in a Hunter. I'd gone along for the ride during a partial air test of Hunter T7 XL617, to check the aileron rigging which had been snagged by someone earlier, then had been checked and NFF'd by the groundcrew.
The captain was the famous Flt Lt 'Puddy' Catt, a legend in his own time. The spitten image of Gert Frobe, 'Puddy' was a typcial 1950s Hunter chap and a true British gent with a wicked twinkle in his eye...
After we finally started up (he'd forgotten the HP cock), off we went and climbed up to about 40K. He then started muttering and dropping each wing in turn, peering intently at the sea 8 miles below. "Ah - there's the bugger!", he said, then we rolled inverted, pulled to about 30 deg nose down before steepening into a high speed transonic dive. Whilst well supersonic, he waggled the control column from side to side and pronounced the ailerons to be perfect. So we recovered to straight and level flight - then he began to decelerate..... Eventually we were well below 100KIAS in very heavy buffet with dust coming up off the floor and the instruments were almost unreadable. "No", boomed 'Puddy' in that rich voice of his, "nothing wrong with these ailerons!" as he again moved the control column from full deflexion one way to the other....
Recovering back to a normal speed, we set off home and I asked him about his manoeuvres before the supersonic dive. "Fishguard to Rosslare ferry, old boy - bound to be full of bog-trotters. Simply had to boom the buggers!".
Great fun - and I hope the old bugger is still propping up the bar in his favourite local pub in Pembrokeshire!
Courtney, any flap above M0.9 and the aircraft was unrecoverable - otherwise no problemo. We often used 23º flap during doggers to obtain improved nose pointing, so it was indeed possible for someone to forget. As possibly happened in the summer of 1976 when a Hunter disappeared without trace during a solo GH trip over the Irish Sea*. First thing to check in a steep dive was 'are the flaps up?'.
A supersonic run was also part of the Hunter AFTS course and the Gnat-Hunter refresher course pre-TWU.
*We were flying an ACM trip and had called the aircraft as a threat before we continued to our exercise area. When we got back, we'd heard it was missing. Now it was quite hazy in the summer of '76 and this was an early morning solo GH trip for the convex pilot. Unusually, the aircraft had full drop tanks. One of the exercises we used to practise was 'low speed looping' at around 320 KIAS entry speed (except for my chum Ozzie, who misheard and tried it at 230....). The low speed loop involved milking it over the top with the flaps, so it's entirely possible that he became disorientated as the heavy-ish aircraft reached the top of the loop. It was easy to reach M0.9, so he could have well experienced the problem. When asked, some of the rest of his course said that they'd never heard of the M0.9 / flap problem - which was astonishing as it was a bit like saying you didn't know that a Chipmunk would swing on take-off. It was something which had certainly been drilled into my feeble brain!