UFO Documentary Film Excerpt:

“Military vs. UFOs” 

(History, New York City)

In this video clip, the UFO Hunters team discusses a 1957 UK 
UFO radar incident:

http://www.history.com/topics/project-blue-book/videos#military-vs-ufos

The unknown object was picked up by two radar systems.

The team concluded that it most likely was a UFO, not a phantom image.

(amazon.com image)