On June 8, 1959, NASA’s rocket-powered X-15 experimental plane made its first glide flight.
The X-15 rocket plane was part of a series of experimental hypersonic aircraft.
This flight marked the beginning of almost a decade of research that explored the altitudes and hypersonic speed at the edge of space.
At maximum speed, the X-15 would fly at Mach 6.7 4,520 miles per hour
The X-15 program had a total of 12 test pilots, including Neil Armstrong, between 1959 and 1968, making 199 flights in the process.
The aircraft flew over a period of almost 10 years.
And with a max altitude of 67 miles, it was even able to reach the edge of outer space in the 1960s.
Source: https://www.space.com/39251-on-this-day-in-space.html