There are dozens of websites just dedicated to this magnificent aeroplane, many with pages and pages of detail. Rather than repeat the detail on these sites, I shall simply attempt to condense the essential details of the aircraft's career into a few paragraphs.
The Lockheed SR-71 was a development of the Lockheed A-12 single seat spyplane designed to meet the USAF's requirement for a strategic reconnaissance aircraft to replace the U-2. First flown in Dec 1964, the major difference between the SR-71 and the A-12 was the addition of an RSO in the SR-71, which resulted in the SR-71 being longer than the A-12 by 1.55m. The SR-71 was also considerably heavier, carried a greater payload and more fuel.
All of the sensors carried by the SR-71 were housed in either the detachable nose or the chine bays. Four different types of nose were available containing either an Optical Bar Camera, a radar nose with either a Goodyear or Loral ground mapping radar, an Advanced Synthetic Aperture Radar (ASARS I) or an empty nose for training or ferry flights. The Operational Objective Cameras (OCCs) housed in the chines were made by Hycon, had a 13-inch focal length and used a 9x9 inch film format. These cameras were withdrawn from use in the early 1970s. The Technical Objective Cameras (TEOCs) were made by the Itek Corporation and initially had a 36-inch focal length which was later increased to 48 inches. Between 1978 and 1980 two aircraft carried 66 inch TEOCs developed by CAI, but little information has been released about these cameras.
In the chine bays the SR-71 carried a number of SIGINT recorders that captured the electronic signature of search radars and SAM systems encountered on sorties. Probably the most sensitive equipment carried in the chine bays was the Defensive Electronic (DEF) systems that were designed to jam or spoof any radar or SAM system as necessary. These systems were continually updated throughout the aircraft's life from the initial DEF A, right through to a programmable system known as DEF A2C. This technology is still in use on current USAF aircraft and consequently little information has ever been released about the DEF system.
The SR-71 was based at Beale AFB in California throughout its career and continually supported routine detachments to Kadena AFB in Okinawa and RAF Mildenhall in the UK. A grand total of 3551 operational sorties were flown by the SR-71 and none was ever shot down. Thirty-two SR-71's were eventually built and only 284 individuals formed the operational crews, all were American citizens.
In 1993 it was decided to retire the SR-71 - the reasons given for the premature retirement was the ability of satellites to carry out the mission and the increasing cost of maintaining the SR-71 fleet. Apart from the cost of maintaining the SR-71 fleet, another factor may have been that may have been taken into consideration was the knowledge that the aircraft had become vunerable. This had been demonstrated on 3 Jun 86 over the Barents Sea, when 6 MiG-31 Foxhounds performed a co-ordinated intercept against an SR-71 that would have subjected the aircraft to an all-angle AAM attack that even the high speed/altitude and ECM capability of the aircraft would have had great difficulty in defeating.
A number of aircraft were briefly retained by NASA for research, but this has now been completed and they are now grounded. All SR-71s have now been dispersed to various museums.
However, it is well known that the orbital characteristics of satellites do not give them the flexibility required for urgent reconnaissance tasks and their predictable tracks (available on the Internet) allow sensitive targets to be hidden from view. Ever wondered why none of the commercial photographic satellites have ever been able to photograph anything of interest at Area 51? Anyway, more on the topic of the replacement for the SR-71 can be found in the Future Reconnaissance Aircraft page.