The development of the MiG-25 began in the 1950s, paralleling American efforts to develop a Mach 3 bomber and interceptor aircraft, including the (ultimately abortive) XB-70 Valkyrie, the XF-103 Thunderwarrior, the Lockheed YF-12, and the XF-108 Rapier. With the first Mach 2 aircraft beginning to enter service, Mach 3 seemed like the next logical step. A variety of roles were considered, including cruise missile carriers, and even a small five- to seven-passenger supersonic transport, but the main impetus was a new high-altitude reconnaissance aircraft and heavy interceptor. If a Mach 3 bomber were to enter American service, it would be nearly invulnerable to Soviet air defense.
The Mikoyan-Gurevich OKB accepted the assignment effective 10 March 1961. Although the XB-70 Valkyrie was cancelled before the new aircraft, which carried the bureau designation Ye-155 (Russian: Е-155), reached the prototype stage, it seemed that the Ye-155 would still be a useful addition to the PVO interceptor force against reconnaissance targets like the SR-71 Blackbird. It was widely believed that the MiG-25 was developed in response to the XB-70. However, A. Belyankov, head of the MiG design bureau confirmed that this was not in fact the case.
The first prototype, which was actually the reconnaissance variant designated Ye-155-R1 by the bureau, made its first flight on 6 March 1964. The prototype interceptor, Ye-155-P1, took to the air on 9 September 1964. Development, which represented a major step forward in Soviet aerodynamics engineering and metallurgy, took several more years to complete. In the meantime, several prototypes, under the cover designation Ye-266 (Russian: Е-266), made a series of record-setting flights in 1965, 1966, and 1967.
As for the XB-70,
In December 1959, the entire program was cut back to a single prototype. This wasn’t the last word on the matter, though, since big weapons procurement efforts acquire a momentum of their own, and by mid-1960 funding for the B-70 program had been restored to a level adequate for as many as a dozen of the bombers.
On 1 March 1961, US President John F. Kennedy announced that the B-70 program was to be scaled back once more. Three aircraft would be completed, including two “XB-70” flight test prototypes and one “YB-70” operational prototype.
Therefore, the specification and request for proposal (or the Soviet equivilant) was issued while the XB-70 was still a viable production program!
And yes, the SR-71 (A-12 originally) was the result of a 1957 CIA request, with Lockheed recieving the order for the aerodynamic & prototype work in 1959 and the order for the first 12 on January 30, 1960… but as this project was a very secret one.
You really have to give me references proving that the USSR had learned of it before March 10, 1961 to convince me that the E-155 was originally ordered to counter the Blackbird!
Yes, there were more reasons than just the Valkyrie for the continued development of the E-155/Mig-25, but it was a major reason the project was started!
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