August 1st 1955; Article 341, also known as the Dragon Lady first took flight...and it wasn't intentional.
As with CIA involvement, , each U-2 had an "article number" assigned, and each U-2 would be referred to with its article number on classified internal documents. The prototype U-2 was known as Article 341,
Article 341's first flight occurred at Groom Lake (Area 51, Dreamland, The Ranch etc...) on this date; August 1st 1955, during what was intended to be only a high-speed taxi test.
As the Dragon Lady approached 70 kts, The sailplane-like wings were so efficient that the aircraft jumped into the air. The test pilot later said, "had no intentions whatsoever of flying", but the Dragon Lady had different plans.
Seven days later, the U-2 reached 32,000 feet, proving that Johnson had met his promised specifications and deadline. By 16 August, the prototype flew at 52,000 feet, an altitude never before reached in sustained flight; by 8 September, Article 341 reached 65,000 feet.
During reconnaissance missions over Russia, The U-2's photographs showed tiny images of MiG-15s and MiG-17s attempting and failing to intercept the aircraft, proving that the Soviets could not shoot down an operational U-2 at altitude. It was reported that the "constant stream of Russian fighters" trying to shoot down the U-2 during overflights was sometimes "so thick" that they interfered with photographs. Repeatedly failing for years to stop the aircraft embarrassed the USSR, which made diplomatic protests against the flights but did not publicize the penetration of Soviet territory.
70 years later, and the Dragon Lady still rules the skies high above...
One interesting note...Due to the highly sensitive nature of the CIA flights, Dragon Lady crews were issued a suicide pill offered before U-2 missions. If put in the mouth and bitten, the "L-pill"—containing liquid potassium cyanide—would cause death in 10–15 seconds. After a pilot almost accidentally ingested an L-pill instead of candy during a December 1956 flight, the suicide pills were put into boxes to avoid further confusion.