The Mojave Desert dawned bright and cold on October 14, 1947. At Muroc Army Air Field, a small orange rocket plane—shaped like a .50-caliber bullet with wings—was hoisted into the bomb bay of a B-29. Captain Charles E. “Chuck” Yeager, who had broken two ribs in a horseback riding accident two days earlier, concealed his pain from all but his friend Captain Jack Ridley. With Ridley’s help he squeezed into the cramped cockpit of the Bell XS-1, which he had named Glamorous Glennis after his wife. At 10:26 a.m., dropped from the B-29 at 20,000 feet, Yeager fired the four chambers of his Reaction Motors XLR-11 rocket engine and climbed. Earlier flights had revealed that shock waves over the elevator would cause a dangerous loss of pitch control as Mach 1 approached. Ridley and Yeager devised a solution: use the moveable horizontal tail, adjusting its angle in tiny increments to control the aircraft without relying on the elevator. At 42,000 feet, Yeager leveled off and relit a third chamber. The Machmeter ticked through 0.98, 0.99, and then, at 43,000 feet, the needle jumped past the scale. Yeager had flown through the invisible wall that many engineers had believed impenetrable. His top speed: Mach 1.06, roughly 700 miles per hour. The flight was smooth—no violent buffeting, no loss of control. When the achievement was finally declassified in June 1948, the Collier Trophy citation declared it “an epochal achievement in the history of world aviation—the greatest since the first successful flight of the original Wright Brothers’ airplane, forty-five years ago.”