During the phase of the cold war, both USSR and USA were trying to disbalance the nuclear balance by achieving the ability of "First strike". The USSR was more keen on achieving this capability by the Intercontinental ballistic missile (ICBM) and on the other hand, the US gave more emphasis on delivering the tactical nuclear warheads from a stealth jet. Lockheed along with Boeing was given the task to develop such stealth jets. After much testing, the Lockheed model was selected by analysts in Pentagon. However, at the same time one more tender came out for a surveillance plane and the specifications for that plane was much similar to the performance stats of the SR-71, thus making SR-71 go through the trial phases for this tender and the rest is history.
SR-71 was first used to take the high definition images of the Soviet nuclear installations. SR-71 took off from the Andrew airforce base and flew right into the Soviet airspace and completed the mission with excellence. The images taken by the SR-71 directed the nuclear policy of the US in late 1970's-1980. The aspect which makes SR-71 different from any other spy jet is its design, which consists of wings expanded away from the fuselage rather towards it which most of the jets have. This makes SR-71 capable of reaching speeds of Mach 3 which is unmatched by any other jets from its era and also makes it capable of reaching altitudes of 100,000 feets which itself is a world record, however, the actual performance parameters of SR-71 are classified even after its retirement in 1999. SR-71 is also the only US military jet which never landed on any NATO airbase because its technology was considered too sensitive even to be shared among the friendly NATO countries.
Then why did such a mission effective military jet retired so early? The reason behind was the operating cost of SR-71 which after factoring in all the expenses came out to be around 200,000$/hour, which was astounding to the standards of early 1990's. Also after the end of cold war, there was a significant cut in the Airforce budget and the top air force brass took the decision to close of the SR-71 program in the lights of climbing maintenance cost of the small fleet of SR-71's. One could imagine the logistics nightmare to maintain the SR-71 fleet by knowing the process of fueling the SR-71 bird, which needed JP7 grade fuel which is transported in a special KC-135Q transporter. Only some of the air force engineers were capable of maintaining the SR-71 bird as it's part and engine were totally different from any other jet in the air force fleet. Also at the end of 1980's USSR had developed SA-10 grumble anti-aircraft missile system, a high-end derivative of S-300 system. The MIG-31 foxhound by Mikoyan corporation was also specially designed to hunt the SR-71, thus affecting the operational effectiveness of the SR-71.
Some of the crazy facts about the SR-71 bird are as following:
1>35 miles per minute or 3,100 feet per second is how fast the SR-71 could fly.
2>170,000 pounds was how much a fully fueled and outfitted Blackbird weighed.
3>85,000 feet is the official Blackbird ceiling, although it supposedly could fly higher.
4>Only32 SR-71s were built.
5>34,000 pounds of thrust was what each of the SR-71’s J-58 engines put out in afterburner (Amazzzzinnng!!).
6>The SR-71's spy equipment allowed it to survey 100,000 square miles per hour of the Earth's surface from an altitude of 80,000+ feet.