As the need arose to replace the Yakovlev Yak-28 Brewer making up the backbone of the Soviet Air Force"s tactical bomber fleet since 1960, the Sukhoi Design Bureau began development of a twinjet tactical bomber known in-house as the T-6. The first prototype (called T6-1) flew in June 1967, featuring delta wings and four lift-jets buried in the fuselage to improve field performance. However, the weight penalty imposed by the lift-jets was deemed unacceptable and the aircraft was radically reworked to feature variable-geometry wings, becoming the Soviet counterpart to the General Dynamics FB-111. The resulting T6-21 entered flight testing in May 1970, subsequently entering production and service as the Su-24. The bomber underwent a progressive refinement and development process, spawing dedicated reconnaissance and ECM variants. To this day, the Su-24 remains the principal Russian tactical bomber. Apart from deployment in East Germany and Poland in the Cold War days, the type has participated in "hot" conflicts as the Afgan War and the First Chechen War. Russian aircraft in action