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The Museum of Flight Is it an extra engine? Is it a UFO? WHAT IS IT? One of the most frequently asked questions in the Museum is why our SR-71 Blackbird has an extra engine on the back of it. Let's bust two myths at once! First, calling our aircraft an SR-71 Blackbird is a common mistake. Even seasoned aviation superfans have glanced at the plane and misidentified it. While it may look like a Lockheed SR-71, this plane is actually a Lockheed M-21, a significantly less famous cousin in the Blackbird family. An easy way to tell the difference is that mysterious third engine-looking contraption on its back. It's not an engine -- it's a drone! Only two M-21s were made, and they were designed by Lockheed's secretive Skunk Works to carry the D-21 drone. The idea was to launch the drone, which was equipped with a camera, off the back of the plane to fly over Soviet territory during the Cold War. The M-21 would turn around before it crossed the border, while the D-21 would keep going. That would technically fulfil the United States' promises not to pilot aircraft over the USSR, since the drone had no pilot, while still giving American intelligence photo surveillance of the region. The program is considered a failure. This M-21 is the only remaining example, as the other plane crashed during testing, killing one of the crew members. A handful of D-21s were flown by Boeing B-52s, but ultimately the drone was shelved in favor of other technology. Learn more about this rare aircraft ➡ https://www.museumofflight.org/.../lockheed-m-21-blackbird Image Description: The Lockheed M/D-21 on display at The Museum of Flight. Image Credit: The Museum of Flight/Ted Huetter