Every air force and navy feels the need for speed. It’s just a fact. When trying to scramble your defending aircraft, time is of the essence and speed is a critical element of that.

Aircraft developers have come a very long way since the development of the first jet engine in the mid-20th century. These days, an airframe that can’t cruise at supersonic speeds might as well be a diesel-powered propeller plane.

It was a long and winding road human engineering took to get to the point where fighter aircraft have the radar cross section of bumblebee. Here are the fastest examples currently in service.

1. Boeing X-37

The Boeing X-37 is an unmanned space drone operated by the US Air Force and boosted into space by NASA. Its mission is to test reusable space technologies, then come back to Earth.

On the way down, the X-37 reenters Earth’s atmosphere at an average speed of 16 times the speed of sound but has come back as fast as Mach 25.

2. MiG-25 Foxbat

The fastest fighter still in service today is the Soviet-built MiG-25. Mikoyan designed this fighter to be a pure interceptor aircraft.

As a result, the Foxbat can sustain a cruising speed of Mach 2.8 and kick it into overdrive with a top speed of 3.2 — not a bad technology for an aircraft that first took off in 1964.

3. F-15E Strike Eagle

The F-15 has been flying for more than 30 years and is set to keep going. The reason is just good design, another aircraft initially designed to catch incoming enemies and destroy them.

The F-15 can fly at a top speed of 3,017 miles per hour, then stop, hit ground targets, and fade away.

4. MiG-31 Foxhound

When the Russians needed something that could try to chase down the vaunted SR-71 Blackbird, they called up the MiG-21 and its Kinzhal hypersonic missiles.

The only problem is that it doesn’t handle as well as its predecessor, the MiG-25. With a top speed of 2,993 miles per hour, it also isn’t as fast.

5. Sukhoi Su-27

The Su-27 is a heavy fighter, designed to be the Soviet Union’s answer to the F-15 program.