It's a mystery that has obsessed many and been the subject of fevered speculation for nearly 45 years. Just why did the experienced world speed record holder Donald Campbell crash so spectacularly on a calm, cold day in January 1967?
Now a new book debunks every theory – from suicide to mystery manifestations in the water – that has grown up around the tragedy.
It was on Coniston Water in Cumbria that Bluebird K7 flipped over at over 300mph, killing Campbell.
The author, Neil Sheppard, claims in his book, Donald Campbell, Bluebird and the Final Record Attempt, that – far from being killed by recklessness or crossing over his own wake – the record holder unknowingly pushed the boat beyond its physical limits.
Using new material, and more than 300 illustrations, Mr Sheppard carried out a comprehensive scientific and engineering analysis of the accident and its causes.
"Campbell was not reckless and at no time, until seconds before disaster, did he think he had exceeded Bluebird's safe operating envelope," Mr Sheppard said.
"He knew he was right on the edge, and was quoted as saying this would be his riskiest record attempt to date, but he did not make his return run too soon, he did not run into any obstacle, or materially adverse water conditions, and he certainly did not have a death wish. The basic fact is the Bluebird just went too fast. No one involved with her engineering was fully aware that the limit was just above the 300mph mark that Campbell was aiming for."
Mr Sheppard teamed up with Dr Keith Mitchell, a retired physicist from the Department of Medical Physics at the Royal Victoria Infirmary in Newcastle. The scientist found that at speeds over 310mph, Bluebird K7 was only marginally stable.
The boat had been built in 1954. The following year Campbell first broke the record with a speed of 202mph. That rose to 260mph by 1959. By 1966, his record stood at 276mph.
On 4 January, Campbell's first run averaged 297.6mph. On the return, he peaked at 328mph and aimed to slow to around 300mph at the end, giving an average of around 310 to 315mph, and a new record average of more than 300mph.
Instead, the boat started to run on the tip of its razor-sharp stabilising fins and rudder, with the hull clear out of the water. It bounced, slowed, then flipped, causing the fatal accident. There is no evidence that it hit an obstacle, the other common theory.
Bluebird is being painstakingly rebuilt by Bill Smith, an engineer and diver who found the sunken wreck in March 2001. It will be displayed in the Bluebird Wing of the Ruskin Museum when it is completed in 2012 or 2013. Campbell's body was also recovered and was later buried in Coniston cemetery.
Campbell's daughter, Gina, said yesterday: "I am so pleased this book puts a stop to all the silly rumours that my father committed suicide or was foolhardy or would do anything stupid. It doesn't change the endgame, but it's a big help."