When it was learned that the Americans were delving into a high-speed, high-altitude Mach 3-capable strategic bomber, it became imperative that Soviet industry develop a similar nuclear-delivery platform to keep pace. Industry mainstays like Sukhoi, Tupolev and Yakovlev entered their designs to fulfill the requirement of 1963 and, in mid-1964, the Sukhoi proposal was selected ahead of the others. The aircraft, slated to become a strategic bomber with reconnaissance capabilities as secondary, was the Sukhoi "T-4" and came to be known under various program names like "Aircraft 100" and "Project 100". As such, the designation "Su-100" became commonly associated with the design.
The T-4 initiative was a complex one requiring a myriad of studies and data collection to be completed as well as massive funding and manpower. High-speed / high-altitude work relied heavily on the use of titanium which was both difficult to work with and expensive to acquire. The bomber was expected to reach speeds beyond the Mach 3 barrier which further complicated design. The end result was an aircraft that mimicked the design lines of the competing XB-70 to a certain extent.
The fuselage was a rather simply-shaped tubular assembly fitting the two-man cockpit at front (seated in tandem), aft of a long nosecone. The nosecone was made to angle downwards during ground running, on approach or during take-off, and was raised when in flight (ala the Concord supersonic passenger jet airliner) t maintain aerodynamic integrity. Unlike the XB-70's six engines, the T-4 showcased only four and these were held in underslung, paired pods with extended intake ramps guiding air into the turbofans. A delta-wing planform was used just as in the XB-70 though the wingtips were fixed and not folding like on the Valkyrie. A sole vertical fin was seated at the tail and, due to the use of the delta-wing planform, no horizontal planes were featured. Canards were added to the sides of the fuselage, aft of the cockpit walls, and this proved another design element already seen on the XB-70. A tricycle undercarriage was fitted featuring eight wheels to each main leg and two wheels for the nose leg. Dimensionally, the T-4 was of a smaller length and wingspan than the XB-70 and exceeded the American design in height by some two meters.
Internally, the aircraft was given an advanced quadruple-redundant Fly-by-Wire (FBW) system for pilot assistance in managing the complicated design in the air. A mechanical back-up scheme was also put in place should the primary FBW systems fail. To reduce the expected long landing rolls, drag chutes would be deployed by the crew - these working in conjunction with standard wheel brakes fitted to each landing gear leg. Standard features like ejection seats and cabin pressurization would be included in production bombers. Propulsion power was from 4 x Kolesov RD-36-41 series turbofan engines developing 35,000lb of thrust each. Performance estimates included a maximum speed of 2,000 miles per hour (Mach 3.0), a cruise speed of 1,865 miles per hour (Mach 2.8), a ferry range out to 4,350 miles and a service ceiling as high as 80,000 feet.
As a strategic bomber it was assumed that the aircraft would carry conventional drop bombs in addition to its expected nuclear war load. For reconnaissance work, cameras would accordingly be fitted and an anti-ship function was also bandied about - meaning that anti-ship missiles were another possible armament fit for the large aircraft. There were no planned onboard defensive cannons as seen in many other Soviet-era Cold War bombers.
A total of four airframes were worked on during the T-4 project with a fifth and six planned. The first was made available for review in the fall of 1971 but did not achieve a first flight until August 22nd, 1972. The Soviet Air Force was already planning for some 250 production-quality bombers built to the standard established by the T-4 prototype. Such a complex instrument required years of testing and the airframe was still being put to its paces into 1974.
With regards to the North American XB-70 program, that aircraft bomber program was cancelled 1961 as it ballooned into an expensive - if promising - venture but advancements in Soviet air defenses began to limit the effectiveness that a high-speed, high-flying bomber would have over the modern battlefield. The two prototypes were relegated to experimental status and a mid-air collision of one of the aircraft in June of 1966 forever stained the Valkyrie's legacy. The other ended its days as a preserved museum showpiece after its flying time had ceased.
The Soviets ultimately followed suit and gave up on their pursuit of a high-speed, high-altitude Mach 3 nuclear-capable bomber when it was deemed that the expensive, technology-laden aircraft actually held little value in the world of advancing missile technology. Furthermore the Soviet Air Force could expand its power quantitatively through procurement of more smaller aircraft of cheaper per-unit design than expend a hefty amount of resources on a contained collection of large bombers. This proved the case as the service elected to push through orders for fighter types instead and the T-4 was terminated on January 22nd, 1974, its performance capabilities never truly tested. The prototype managed just over ten hours in the air in its ten flights completed.
The sole completed flyable prototype - the next three were never finished and the fifth and sixth forms never materialized beyond their paper stage - joined the XB-70 as a preserved museum showpiece, it residing at the Central Air Force Museum outside of Moscow along with many other Cold War-era flying artifacts.