By Tim Kirkpatrick
The SR-71 Blackbird was developed by Lockheed Martin as a long-range reconnaissance aircraft that could hit air speeds over Mach 3.2 ( 2,455 mph) and climb to an altitude of 85,000 feet.
In March 1968, the first operational Blackbird was flown out of Kadena AFB in Japan. With the Vietnam war in full swing, the intent was to conduct stealth missions by gathering photographs and electronic intelligence against the enemy. The crew would fly daily missions into sensitive areas where one slight mishap could spark an international incident.
After climbing to 60,000 feet, the crew switched off its communication system so that only a select few would know the mission’s target. The aircraft didn’t always rely on its speed for defense; it was equipped with a jammer that would interrupt the enemy’s communication between the radar site and the missile itself.
On occasion, the enemy would fire missiles without radar guidance, which would sometimes get so close that the pilots could spot the passing missiles 150-yards away from inside the cockpit
http://www.wearethemighty.com/military-life/5-countries-that-tried-to-shoot-down-the-sr-71-blackbird-and-failed.