My brother, who joined the RAF in '61, was told there were two raids at different times. The first involved Vulcans* (I think) trying to go in above the American radar cover and succeeding. The Americans then worked hard to improve the high coverage of their Air Defence Radars and about a year later, Victors* were sent in at low level and succeeded in penetrating BELOW the American radar cover!
I heard later from an officer at the Strike Command Bombing School at Lindholme, that Chapman Pincher, the defence journalist, was on board one of the raiders.
*Could have been the other way round; my brother told me about it over 40 years ago