There is much to say about the Lockheed SR-71 Blackbird even though many of its secrets remain classified. Before the SR-71 Blackbird came to be, the United States Air Force made several prototypes for a variety of roles. Among those variations was the Lockheed YF-12 which was planned as a high-speed interceptor.
While creating the A-12, the teams at Skunkworks imagined a weaponized version of the jet. One design incorporated a two-seat version of the aircraft giving the second crewman the ability to fire air to air missiles. The YF-12 was a highly successful aircraft reaching the record speed and record altitude which would only be surpassed when the SR-71 Blackbird debuted.
The YF-12 was originally equipped with the ability to carry 250-kiloton nuclear warheads but this was later replaced with radar jamming technology. The YF-12 was used by NASA to record date but ultimately the program was shut down in 1970 as the Skunkworks proceeded ahead with the SR-71. Only three YF-12 aircraft were built and two of them were destroyed in training accidents.
The film of the crews testing the YF-12 at Edwards Air Force shortly after its public debut can be seen in this footage.