During the latter years of the Cold War, Soviet Frontal Aviation units employed a mixed fleet of battlefield interdic- tion and theatre strike aircraft. The most potent of these was the Sukhoi Su-24 Fencer, conceptually similar to a smaller F-111, supplemented by the even smaller Su-17 Fitter, a vari- able geometry derivative of the Su-7, and the MiG-23BM and MiG-27, both derivatives of the variable geometry MiG-23 interceptor. Soviet doctrine during that period was being seriously challenged by large numbers of US and NATO teen series fighters, especially the F-15 and F-16. While Frontal Avia- tion MiG-29 and Su-27S fighters were to win the air battle, allowing the less agile Su-24, Su-17, MiG-23BM and MiG-27 to survive and attack their targets, it was evident to Soviet plan- ners that replacements for these strike aircraft would need to be capable of surviving close contact with the F-16 and especially the F-15. The Sukhoi bureau was intimately familiar with the prob- lem to be solved, as designers of the earlier Su-7, and later Su-17/22 and Su-24, they had first hand exposure to the often conflicting design requirements of these roles. Early Sukhoi thinking concentrated on adaptations of the baseline Su-27UB tandem seat trainer, a model since then implemented in the F-15E-like Su-30MK series exported to China and India. Frontal Aviation thinking was however that the crew station approach used in the Su-24 worked better for the high workload and potentially long endurance strike roles. Conceptual design of the Su-27IB as an Su-24 replace- ment began in 1983.