The length of the model is 13.00 inches and the length of the base is 17 inches 

In 1966, Campbell decided to once more try for a water speed record; a target of 300 mph (480 km/h).

K7 was fitted with a lighter and more powerful Bristol Siddeley Orpheus engine, taken from a Folland Gnat jet aircraft, which developed 4,500 pound-force (20 kN) of thrust. The new K7 had modified sponsons, a vertical stabiliser and a new, streamlined canopy for the pilot.The boat returned to Coniston for trials in November 1966. These did not go well; the weather was appalling and K7 suffered an engine failure when her air intakes collapsed and debris was drawn into the engine. Eventually, by the end of November, some high-speed runs were made, but well below the existing record. Problems with the fuel system meant that the engine could not develop maximum power. Eventually, by the end of December, this problem was fixed and better weather was waited for to mount an attempt.

On 4 January 1967, Campbell was killed when K7 flipped over and disintegrated at a speed in excess of 300 mph (480 km/h).^[1] Bluebird had completed a perfect north-south run at an average of 297.6 mph (478.9 km/h), and Campbell used a new water brake to slow K7 from her peak speed of 315 mph (507 km/h). Instead of refuelling and waiting for the wash of this run to subside, as had been pre-arranged, Campbell decided to make the return run immediately. 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 over the rough water, and the boat started tramping from sponson to sponson. 150 yards from the end of the measured mile, K7 lifted from the surface and took off at a 45-degree angle. She somersaulted and plunged back into the lake, nose first. The boat then cartwheeled across the water before coming to rest. The impact broke K7 forward of the air intakes (where Donald was sitting) and the main hull sank shortly afterwards. Campbell had been killed instantly. Mr. Whoppit, Campbell's teddy bear mascot, was found among the floating debris and the pilot's helmet was recovered. Royal Navy divers made efforts to find and recover the body but, although the wreck of K7 was found, they called off the search without locating his body.

Campbell's last words on his final run were, via radio intercom:

The cause of the crash has been variously attributed to Campbell not waiting to refuel after doing a first run of 297.6 mph (478.9 km/h) and hence the boat being lighter; the wash caused by his first run and made much worse by the use of the water brake; and potentially a cut-out of the jet engine caused by fuel starvation. Some evidence for this last possibility may be seen in film recordings of the crash - as the nose of the boat climbs and the jet exhaust points at the water surface no disturbance or spray can be seen at all.