On 4 January 1967, Campbell mounted his record attempt. Bluebird had completed an initial north–south run at an average of 297.6 mph (478.9 km/h), and Campbell used the new water brake to slow K7 from a peak speed of 311 mph (501 km/h) when he left the measured kilometre. Instead of coming to a stop and opting to refuel, he decided to perform a quick turnaround and immediately head back up the course before the wash of his first run had time to be reflected back towards the centre of the lake. Both options had been discussed in the pre attempt briefing.
The second run was even faster; as K7 passed the start of the measured kilometre, she was travelling at over 320 mph (510 km/h). However her stability had begun to break down as she travelled at a speed she had never achieved before, and the front of the boat started to bounce out of the water on the starboard side. 150 yards (135 metres) from the end of the measured kilometre, K7 lifted from the surface and after about 1.5 seconds, gradually lifted from the water at an ever-increasing angle, then took off at a 90-degree angle to the water surface. She somersaulted and plunged back into the lake, nose first, then cartwheeled across the water before coming to rest. The impact broke K7 forward of the air intakes (where Campbell was sitting) and the main hull sank shortly afterwards.
Campbell had been killed instantly. Mr Whoppit, his teddy bear mascot, was found among the floating debris and his helmet was recovered. Royal Navy divers were able to locate the wreck of K7, but called off the search for Campbell’s body after two weeks.[