The Su-27 was developed primarily for Russia's air-defense interceptor forces. Work on the T-10 design that led to the Su-27 began in 1969. The requirement was for a highly maneuverable fighter with very long range, heavy armament and modern sensors, capable of meeting the F-15 on equal terms.
The first prototype T-10 Flanker-A flew in 1977. The early flight development programme revealed serious problems that led to a total redesign; the resulting T-10S-1 flew in 1981. The single-seat Su-27 Flanker-B eventually entered operational service in 1985 and remains a formidable interceptor.
Its heavy armament of up to 10 air-to-air missiles gives excellent combat persistence; outstanding maneuverability, coupled with a helmet sight to cue agile R-73 missiles also make it a potent close combat fighter, and its large internal fuel capacity confers a very long range that allows the Su-27 to escort Su-24 interdictors.
All operators also use Su-27UB Flanker-C two-seat trainers. This retains full combat capability and has been developed further.
The Su-27K is a naval fighter variant that has the Russian naval aviation service designation Su-33. A total of 24 production aircraft has been built to date; the type made its first deployment on carrier Kuznetsov in 1995.
Sukhoi is developing variants for the reconnaissance and electronic warfare/command post roles. In 1988 Sukhoi flew a significantly developed single-seat version of the Flanker-B as the Su-27M. This was proposed as a super agile Su-27 primarily for counter-air missions, but also with a greatly expanded air-to-surface capability. The Su-27M was later redesignated Su-35 by Sukhoi and offered as a MiG-29/Su-27 replacement. Its development was halted after 11 prototype and pre-series/technology demonstrator aircraft had been built. The last Su-35 (711) was fitted with thrust-vectoring nozzles to confer even higher levels of maneuverability. This aircraft was actively proposed for the Russian air force as the Su-37.