In the 1950s North American Aviation company designed the most spectacular strategic nuclear bomber - B-70. This supersonic giant had six engines capable of reaching Mach 3+ at an altitude of 70.000 feet (21.000 m -  the middle of the Stratosphere). But by the 1960s with the improved SAM technology and the introduction of ICBMs this bomber was to costly to made so the B-70 Bomber program was canceled, yet  North American Aviation company, for scientific purposes built 2 experimental aircrafts XB-70A Valkyrie. During test flights only two minor incidents happened: one of the landing gears had issues lowering and paint chipped away. A 1st in aviation were the adjustable wing tips that could be lowered or raised if needed.

ED97-44244-2 This photo shows XB-70A #1 taking off on a research flight, escorted by a TB-58 chase plane. The TB-58 a prototype B-58 modified as a trainer had a dash speed of Mach 2. This allowed it to stay close to the XB-70 as it conducted its research maneuvers. When the XB-70 was flying at or near Mach 3, the slower TB-58 could often keep up with it by flying lower and cutting inside the turns in the XB-70's flight path when these occurred.1960s NASA Photo / North American photo

On 8 June 1966, XB-70A Valkyrie #2 collided in midair with a F-104 jet. NASA Chief Test Pilot Joe Walker (F-104 pilot) and Carl Cross (XB-70 co-pilot) were killed. Al White (XB-70 pilot) ejected, sustaining serious injuries.

Since 4 February 1969, XB-70A Valkyrie #1 is on display at  National Museum of the United States Air Force at Wright-Patterson AFB near Dayton, Ohio. 

EC84-28218 Moments before the F-104 and XB-70 collided, the ill-fated formation flight centered on the XB-70, flanked by a T-38A, F-4B, the F-104 orange tail and a YF-5A.June 8, 1966 NASA Photo

ECN-1008 This is a close-up photo of an XB-70A taken from a chase plane. The XB-70 had a movable windshield and ramp. These were raised during supersonic flight to reduce drag. When the pilot was ready to land, he lowered the assembly to give both him and his copilot a clear view of the runway. 1965 NASA Photo

ED97-44244-1 Photo of the XB-70 #1 cockpit, which shows the complexity of this mid-1960s research aircraft. On the left and right sides of the picture are the pilot's and co-pilot's control yokes. Forward of these, on the cockpit floor, are the rudder pedals with the NAA North American Aviation trademark. Between them is the center console. Visible are the six throttles for the XB-70's jet engines. Above this is the center instrument panel. The bottom panel has the wing tip fold, landing gear, and flap controls, as well as the hydraulic pressure gages. In the center are three rows of engine gages. The top row are tachometers, the second are exhaust temperature gages, and the bottom row are exhaust nozzle position indicators. Above these are the engine fire and engine brake switches. The instrument panels for the pilot left and co-pilot right differ somewhat. Both crewmen have an airspeed/Mach indicator, and altitude/vertical velocity indicator, an artificial horizon, and a heading indicator/compass directly in front of them. The pilot's flight instruments, from top to bottom, are total heat gage and crew warning lights; stand-by flight instruments side-slip, artificial horizon, and altitude; the engine vibration indicators; cabin altitude, ammonia, and water quantity gages, the electronic compartment air temperature gage, and the liquid oxygen quantity gage. At the bottom are the switches for the flight displays and environmental controls. On the co-pilot's panel, the top three rows are for the engine inlet controls. Below this is the fuel tank sequence indicator, which shows the amount of fuel in each tank. The bottom row consists of the fuel pump switches, which were used to shift fuel to maintain the proper center of gravity. Just to the right are the indicators for the total fuel top and the individual tanks bottom. Visible on the right edge of the photo are the refueling valves, while above these are switches for the flight data recording instruments. 1965 NASA Photo

ECN-1814 This photo shows the XB-70A parked on a ramp at Edwards Air Force Base in 1967. Originally designed as a Mach 3 bomber, the XB-70A never went into production and instead was used for flight research involving the Air Force and NASA's Flight Research Center FRC, which was a predecessor of today's NASA Dryden Flight Research Center. The aircraft's shadow indicates its unusual planform. This featured two canards behind the cockpit, followed by a large, triangular delta wing. The outboard portions of the wing were hinged so they could be folded down for improved high-speed stability.1967 NASA Photo

EC68-2101 The figure standing on the ramp provides a relative size comparison with the XB-70A aircraft. Six large nozzles for the General Electric engines are shown between and below the two large vertical tails.The XB-70A, capable of flying three times the speed of sound, was the world's largest experimental aircraft in the 1960s. Two XB-70A aircraft were built. The number one XB-70A was flown by the NASA Flight Research Center now NASA Dryden, Edwards, California, in a high speed flight research program. The second aircraft was lost in a mid-air collision on June 8, 1966 with a NASA F-104.1968 NASA Photo

ECN-792 Viewed from the front the #1 XB-70A 62-0001 is shown climbing out during take-off. Most flights were scheduled during the morning hours to take advantage of the cooler ambient air temperatures for improved propulsion efficiencies. The wing tips are extended straight out to provide a maximum lifting wing surface.The XB-70A, capable of flying three times the speed of sound, was the world's largest experimental aircraft in the 1960s. Two XB-70A aircraft were built. Ship #1 was flown by NASA in a high speed flight research program. August 17,1965 NASA Photo

ECN-2128 In this view the #1 XB-70A 62-0001 is in a level cruise flight mode at a relative high altitude judging from the darkness of the sky.The XB-70A, capable of flying three times the speed of sound, was the world's largest experimental aircraft in the 1960s. Two XB-70A aircraft were built. Ship #1 was flown by the NASA Flight Research Center now NASA Dryden, Edwards, California, in a high speed research program.1968 NASA Photo

EC68-2131 In this photo the #1 XB-70A 62-0001 is viewed from above in cruise configuration with the wing tips drooped for improved controllability.The XB-70A, capable of flying three times the speed of sound, was the world's largest experimental aircraft in the 1960s. Two XB-70A aircraft were built. Ship #1 was flown by the NASA Flight Research Centernow NASA Dryden, Edwards, California, in a high speed flight research program.1968 NASA Photo