The U2 was produced in 1955 by Lockheed's Skunk Works for aerial reconnaissance missions over the Soviet Union. The proposal to build a plane that could fly 70,000 feet came from the need to fly beyond the reach of Soviet fighters, missiles, and radar; basically, anything that could threaten it.
The U.S. Air Force solicited designs from several aircraft companies, including Lockheed before settling on the winning concept. Lockheed's first try, by Clarence "Kelly" Johnson—its best aeronautical engineer at the time—included the base of an XF-104 with elongated wings and a shortened fuselage named CL-282. The design was essentially a jet-powered glider; it had a single jet engine, had no landing gear, but could reach an altitude of 73,000 feet. Gen. Curtis LeMay famously walked out during the design's presentation, saying that he was not interested in an airplane without wheels or guns.
After the rejection and several iterations later, Lockheed submitted the design for the U2 spy plane, nicknamed "Dragon Lady." Its basic design is still in use today, thanks to its meticulous Programmed Depot Maintenance inspections every 4,700 flight hours.
While the aircraft didn't fully adopt the no wheels design, it did find a compromise. Instead of the typical tricycle landing gear used in most aircraft, the U2 uses a bicycle configuration with a forward and aft set of landing wheels. This minimalist approach and other design elements make the airplane lighter, which is one of the main reasons the airplane can cruise at such a high speed.
This video shows spectacular footage from the cockpit of the U2 spy plane at 70,000 feet above the Earth. Watch: