Two Typhoon jets scrambled to an aircraft which had lost communications caused a sonic boom in the early hours of Sunday.
The RAF said the fighter planes were deployed from RAF Coningsby in Lincolnshire shortly before 4.10am.
The aircraft were the cause of an explosion-like sound which was heard across vast swathes of the South East, with Hertfordshire Fire and Rescue receiving a "large number" of calls.
People living in Essex, west London and Stevenage were among those tweeting to say they had been woken up by the noise.
An RAF spokeswoman said: "Two Typhoon fighter aircraft from RAF Coningsby were scrambled at 0409 this morning, as part of the UK's Quick Reaction Alert procedures, after an aircraft lost communications in UK airspace.
"The aircraft was intercepted and its communications were subsequently re-established. The Typhoons are returning to their base."
