SR-71A S/N 61-7959, also known as "Big Tall", came off the assembly line like any other SR-71 when it was rolled out on 16 Aug 1965. But it has a unique trial modification which added 9 feet (2.7m) beyond the tail to carry a new optical bar camera as well as more electronic countermeasures. On 3 December 1975, the "Big Tall" flew for the first time. The tests demonstrated that there was little performance loss, but that the new sensor equipment proved of little advantage. The program was dropped. This aircraft was last flown on 29 October 1976 and is the only "Big Tall" in existence.