On August 27, 1937, Captain George E. T. Eyston breaks his own automobile land speed record at the Bonneville Salt Flats in Utah, raising the mark to 345.49 mph.
Located approximately 80 miles west of Salt Lake City, Utah, the Bonneville Salt Flats were formed by the evaporation of a huge Ice Age-era lake. Near the end of the 19th century, the flats hosted a bicycle competition arranged as a publicity stunt by the publishing magnate William Randolph Hearst. Then, in 1914, the daredevil racer Teddy Tezlaff drove his Blitzen Benz vehicle at 141.73 mph to set an unofficial land speed record at the flats. Bonneville truly took off as a racing destination thanks to the efforts of Utah native Ab Jenkins, who set several endurance speed records there beginning in 1925, driving a Studebaker dubbed the Mormon Meteor. In 1935, the British racing legend Sir Malcolm Campbell set a world land speed record of 301.126 mph in his famous Bluebird, and since then the flats became the standard course for land speed record attempts.
Drivers who attempted to set the world land speed record, or the fastest speed traveled on land in a wheeled vehicle, had to complete two mile-long runs in opposite directions, within a space of sixty minutes. George Eyston, an engineer and retired British Army captain, had set the previous record of 311.42 mph at Bonneville in November 1936. On his August 27 run, he hit 347.49 mph on the outbound trip and 343.51 on the return; his new record, 345.49, was the average of the two. As Eyston told the press at the time, he did not even bring his vehicle, the Thunderbolt, to full throttle to achieve the record-setting speed: "I had a very comfortable ride and not once did I feel there was any danger... I wanted to be certain I set a new record, but I also wanted to be sure that the car and I got through in good shape."
By September 1938, Eyston had raised the land speed record to 357.5 mph. In a lecture he delivered that month, Eyston described his built-for-speed Thunderbolt as having two 2,000-horsepower Rolls Royce motors geared together; the vehicle measured 35 feet long and weighed nearly 7 tons. One of Eyston's rivals, John Cobb, set a new world land speed record of 394.194 mph in 1947 at Bonneville in a car with a piston engine; thereafter, most record holders have driven jet- or rocket-powered vehicles. In October 1997, a twin turbofan jet-powered car dubbed ThrustSSC achieved 763.035 mph (the first supersonic world land speed record) over one mile at Nevada's Black Rock Desert.