This was Douglas' prototype for the US Army's super fighter program, though when it was compared to it's competitors it was larger and heavier than all of them, though the SFD was actually pretty quick for it's size, this suprising speed made it a good candidate for Super fighter, but after substantial flight tests it was found out that it had poor handling in low speeds and low altitude, this wasn't a problem for fighting jets this was a problem when the pilot came into land or to takeoff, out of the 24 test flights 15 ended in some sort of crash this led it to become unpopular with both pilots and it's designers (it's a little unstable at low speeds)