Human engineering has driven aircraft to extreme speeds from early jet-powered aircraft that surpassed 600 km/h to experimental hypersonic craft reaching Mach 10-plus. Throughout aviation history, there has been no shortage of aircraft challenging conventional wisdom concerning propulsion, aerodynamics, materials, altitude and handling qualities. Most of these aircraft were built to conduct research, gain new knowledge, take reconnaissance photographs, intercept targets or simply to explore the boundaries of aircraft performance.

Read more this deep dive: The 10 Fastest Aircraft Ever Built This ranking examines ten of the fastest aircraft ever designed, from experimental research craft and rocket-powered aircraft to high-speed spy planes, strategic designs, and lethal military interceptors. Every aircraft provided a breakthrough engineering answer, be it for a new type of engine, heat-resistant body structure, aerodynamic refinement, or high-altitude operation. All show how aerospace engineering often sought to break the speed barrier.

1. HTV-2 Falcon

The top-secret HTV-2, or Falcon, program was under way at DARPA. It was an advanced experiment in hypersonic glide vehicles intended to fly more than 10 times the speed of sound. The plan was to send an unmanned vehicle aloft using a rocket-powered booster, then glide it across the sky at hypersonic speeds, allowing it to maneuver and control as it entered the boundary layer or atmosphere where intense forces of heat and air become the greatest engineering challenges.

HTV-2 Falcon Key Points:

• Developed under DARPA’s Falcon Project
• Designed for hypersonic flight
• Capable of exceeding Mach 10
• Uses advanced carbon composites
• Studies extreme thermal protection

The body of the HTV-2 was constructed from advanced carbon composite materials capable of withstanding the enormous accelerations and thermal stresses of hypersonic flight. Temperatures on the body of the vehicle could exceed 1,930 C, well above what a steel structure could tolerate. While there were technical failures during the first few flights, the data returned from the test vehicles was valuable in continuing to advance aerospace technology.

2. NASA X-43

The X-43 aircraft designed and manufactured by NASA was developed as part of the Hyper-X program to study hypersonic aerodynamics and the technology of the scramjet engine. This pilotless aircraft became world-famous by reaching a speed of almost Mach 9.6, i.e., roughly 10,240 km/h, during the third and last flight in November 2004 a highlight in experimental jet aircraft with implications for the air-breathing propulsion systems.

NASA X-43 Key Points:

• Developed under NASA’s Hyper-X
• Unmanned experimental aircraft
• Reached approximately Mach 9.6
• Used hydrogen-fueled scramjet propulsion
• Flew around 110,000 feet

The X-43 employed a different kind of jet engine known as a scramjet that squeezed the incoming air for the hypersonic ride, utilized the air to burn its own on-board hydrogen, and then ignited that mixture. Prior to engine ignition and powered flight, the vehicle was dropped from a B-52 and a Pegasus booster. After it reached the correct altitude and speed, the booster was detached and it continued its flight using its scramjet. The tests proved the potential of scramjet engines for future hypersonic vehicles and space access vehicles.

3. North American X-15

However, that is still one of the most radical crewed aircraft ever built. The X-15 is an aircraft powered by rockets, which came into being in October 1967 by a test pilot William “Pete” Knight that reached the aircraft to the Mach 6.7 speed 7,000 km/h. The plane was taken on the wing of a B-52 bomber, and was launched into the air for a series of tests, 199 flights in all over the space of nearly ten years. It was truly a game-changer, breaking new ground on what the aircraft of the future could do.

North American X-15 Key Points:

• Rocket-powered research aircraft
• Reached Mach 6.7
• Air-launched from a B-52
• Completed 199 missions
• Reached above 50-mile altitude

The X-15 had a thick wedge-shaped tail which made the aircraft stable and controllable at high speeds. Four pilots flew in excess of 50 miles (80 km) in altitude, with three earning astronaut wings according to the criteria then in effect. The program not only set speed records, but provided many insights in high speed aerodynamics, structural cooling, and the effects of high speed flight on humans. The X-15 experience eventually supported the United States’ subsequent human space flight programs, such as Mercury, Gemini, Apollo, and the Space Shuttle.

4. Lockheed SR-71 Blackbird

A legendary aircraft, the Lockheed SR-71 Blackbird, it is one of the most recognized high speed aircraft ever developed and the fastest air breathing crewed aircraft in service. Developed by Clarence “Kelly” Johnson along with Lockheed Skunk Works, the reconnaissance aircraft was designed to operate at speeds of Mach 3.3 and above 80,000 feet. Its high speeds and altitude give it the range to quickly fly reconnaissance missions and stay out of the attacker’s reach.

Lockheed SR-71 Blackbird Key Points:

• Designed by Kelly Johnson
• Reached around Mach 3.3
• Operated above 80,000 feet
• Built mainly from titanium
• Used twin J58 engines

The aircraft was primarily made of titanium, as its skin could reach 600 degrees F during sustained high-speed flight. It employed two Pratt & Whitney J58 engines that performed in a varied manner as the aircraft’s speed increased; the engines acted as turbojets at lower speeds but began to resemble a ramjet at higher Mach numbers. The Blackbird’s speed was a defensive tool in itself: As soon as a surface-to-air missile was detected, the aircraft could accelerate and, using its exceptional speed and altitude, outrun the threat. Its ability to combine speed, altitude and reconnaissance made the Blackbird a marvel in aerospace engineering.

5. Lockheed YF-12

The Lockheed YF-12 was an A-12 design prepared as a high-speed, high altitude interceptor to meet the threat of high-flying enemy bombers. It was a two-seat aircraft that first flew in 1963, set an official speed record of 3,331.5 km/h on 1 May 1965, and flew at altitudes above 80,000 feet. It was an aircraft of incredibly high speed and high-tech missile and radar ability, not a typical aircraft of most of its lifetime.

Lockheed YF-12 Key Points:

• Based on the A-12 airframe
• Twin-seat interceptor prototype
• Exceeded 3,300 km/h
• Operated above 80,000 feet
• Carried three internal missiles

The YF-12 was equipped with an advanced fire-control radar and was designed to carry 3 internal air-to-air missiles. Despite being a highly capable combat aircraft, the overall military interceptor project was axed due to budget restrictions and other competing military priorities. Only three aircraft were built, and after the termination of the aircraft’s use in the defense program, NASA continued to utilize the remaining aircraft for research purposes until 1979. These research flights were instrumental in studies of high-speed, high-altitude aerodynamics and supersonic control.

6. North American XB-70 Valkyrie

The North American XB-70 Valkyrie was a Mach 3+ strategic bomber with high-altitude performance and a maximum payload capacity, built during the 1950s. An experimental aircraft 200 feet in length, it had a huge delta wing composed of titanium and stainless steel and six turbojets with afterburners. The aircraft is said to have set a top recorded speed of around 3,250 km/h (almost Mach 3.8), making it one of the most intense high-performance aircraft ever constructed.

North American XB-70 Key Points:

• Designed as a strategic bomber
• Nearly 200 feet long
• Used six turbojet engines
• Reached Mach 3.8
• Used compression lift

One of the most innovative aspects of the Valkyrie was its utilization of compression lift. This technique enabled the aircraft to ride its own shock wave at very high speeds and greatly enhance its aerodynamic efficiency. The Valkyrie’s high-altitude, high-speed bomber concept was rendered obsolete by advances in surface-to-air missiles. The XB-70’s production program was therefore cancelled and the two aircraft were used for research. High speed tests yielded useful information that led to future aircraft, including the B-1 and experimental projects related to speed of the next era’s air transport.

7. Bell X-2 Starbuster

Bell X-2 Starbuster In order to better understand the challenging aerodynamics and heating problems that occurred when aircraft entered into Mach 2. Bell Aircraft, the U.S. Air Force and NACA collaborated on the development of a swept wing research aircraft fitted with a Curtiss-Wright XLR25 rocket powerplant delivering 67 kilonewtons of thrust. The first powered flight occurred in 1955 and, piloting Frank “Pete” Everest, the aircraft later achieved 3,050 km/h at 20,764 m altitude.

Bell X-2 Starbuster Key Points:

• Built for Mach 2–3 research
• Used a rocket engine
• Reached Mach 3.1
• Had swept wings
• Studied high-speed stability

But Starbuster kept raising the bar, as pilot Milburn Apt hit Mach 3.1 (3,369km/h) on 27 September 1956, making him the first human to ever fly three times the speed of sound. Issues emerged with the aircraft’s controls after the craft reached its maximum speed and it plummeted to the ground. The X-2 only flew 20 missions, but it provided important data on inertia coupling, how well the plane’s aerodynamics held up at high speed, and the thermodynamics of high speed flight. Those lessons were built upon by future high speed aircraft development.

8. Mikoyan-Gurevich MiG-25 “Foxbat”

Mikoyan-Gurevich MiG-25 “Foxbat” The MiG-25 “Foxbat” was a dedicated high-altitude interceptor and reconnaissance aircraft. Introduced into service in 1964, the Soviet aircraft was built with a heavy nickel-steel alloy to withstand the intense temperatures of high speed travel and was officially capable of a top speed of around Mach 2.8 (~3,000 km/h) but could reach Mach 3 in short bursts, a feat which would severely harm the engines.

Mikoyan-Gurevich MiG-25 Key Points:

• Designed for high-altitude interception
• First flew in 1964
• Official limit around Mach 2.8
• Used nickel-steel construction
• Led to the MiG-31

The Foxbat was able to operate at about 23,000 meters and a modified one in 1977 made it to 37,650 meters. Its large wings initially gave Western intelligence an exaggerated impression of its fighting ability, and the aircraft would influence the design philosophy of the later American F-15 Eagle. The MiG-25 would eventually be superseded by the MiG-31 Foxhound, which was also capable of high speeds while featuring more modern systems like the Zaslon phased-array radar. With over 1,000 built, the MiG-25 became one of the most important symbols of high-speed Cold War aviation and one of the fastest military aircraft ever mass-produced.

9. Mikoyan-Gurevich Ye-152/ Ye-166

Mikoyan-Gurevich Ye-152 The Ye-150 test family was a series of experimental aircraft that included the Mikoyan-Gurevich Ye-152 prototype, as the most expensive aircraft prototype. The large and heavy interceptor was built to explore technologies such as weaponry, avionics and high-speed capabilities. On April 21, 1961, the Ye-152 prototype, which weighs in at over 12,300kg (27,123 pounds), was a much more than the MiG-21F.

Mikoyan-Gurevich Ye-152/ Ye-166 Key Points:

• Part of the Ye-150 family
• First flew in 1961
• Weighed over 12,300 kg
• Used Tumansky R-15 engine
• Reached 2,681 km/h

The propulsion was derived from a single Tumansky R-15 turbojet and powered the aircraft to a maximum speed of around 2,681 km/h (1,665 mph). However, engine reliability issues hampered tests and nearly hindered the aircraft’s development potential. Nevertheless, the Ye-152 proved to be a valuable tool in collecting data about performance needs for a high-speed interceptor and even set some world’s speed records (registered under the designation Ye-166). The aircraft thus remained an important step on the road to the development of the future Soviet high-speed interceptor.

10. McDonnell Douglas F-15 Eagle

The McDonnell Douglas F-15 Eagle made its maiden flight in July 1972. It was designed and built as an air-superiority fighter for the US Air Force. Propelled by two afterburning turbofans producing a combined total of 105.7 kilonewtons of thrust, the fighter has achieved a speed of around 2,655 km/h (Mach 2.5). This was achieved in dramatic fashion by an F-15A Streak Eagle in 1977 which broke eight time-to-climb records, including climbing to an altitude of 98,425 feet in less than three and a half minutes.

McDonnell Douglas F-15 Eagle Key Points:

• First flew in July 1972
• Designed for air superiority
• Reaches Mach 2.5
• Set eight climb records
• Evolved into the F-15EX

The F-15 became one of the most successful modern fighters, claiming over 100 air-to-air kills with no air-to-air losses on record. The aircraft has been operated by the US Air Force as well as Israel, Japan, and Saudi Arabia. The original Eagle was very much an air dominance aircraft but its design left a strong basis for subsequent developments like the twin-seater F-15E Strike Eagle. The aircraft platform itself has evolved over the decades with the current F-15EX Eagle II not only carrying the F-15 family into a new generation of service but also carrying on the Eagle tradition of high-performance aircraft.