The Cold War Heats Up, and Conventional Weapons Become the Focus
Throughout the 1950s and much of the 1960s it was assumed that any future conflict between the Soviet Union and United States would rapidly escalate to include the use of nuclear weapons. Because of this, both sides engaged in a nuclear arms race that would eventually lead to tens of thousands of warheads being deployed on hair trigger alert around the world.
But the Vietnam war and a series of border clashes between the Soviet Union and the People's Republic of China showed that superpowers might still fight more traditional, conventional conflicts involving tanks, planes, and ships. The Cuban Missile Crisis too demonstrated the dangers of relying on nuclear deterrence alone. So by the mid to late 1960's both superpowers began to develop new generations of conventional weapons and moved to compete with one another in the air, on land, and at sea.
Bombers by this time were becoming ever more vulnerable to surface to air missiles and fast interceptors. But they were still considered to be valuable long range strike aircraft and a key part of a nations' nuclear deterrent. Even as the Cold War opponents began designing a new generation of conventional weapons they both realized that their traditional big, slow, high altitude bombers were no longer capable of surviving in a rapidly changing military environment.
The Soviet Union had an additional problem. In addition to needing an airframe to replace the aging Tu-16 Badger and Tu-95 Bear models in the nuclear strike role some kind of counter had to be developed for the growing threat posed by United States carrier battle groups at sea. The Soviet Union's sea based deterrent on board ballistic missile submarines could be threatened by US carriers operating near to the Soviet coast. The Soviet Navy was no match for the US Navy and so the Soviets felt at risk of losing both their aerial deterrent and submarine deterrent if a war broke out. A weapons system was needed that could both fend off US carrier groups and deliver nuclear strikes.