The Soviets did not deploy any real substantial low-observable aircraft during the Cold War, which was ironic because one of the major scientific breakthroughs on radar refraction, Pyotr Ufimtsev's 1962 paper Method of Edge Waves in the Physical Theory of Diffraction was came from the Moscow Institute for Radio Engineering. This unclassified paper found its way into the US via the USAF's System Command's Foreign Technology Division in 1971. Ufimtsev's paper helped Lockheed's Skunk Works' in its ECHO 1 computer program designed to predict radar cross sections (RCS). The ECHO 1 software was incredibly useful for the development of the Have Blue technology demonstrator and other first-generation low-observable aircraft.

As to why the Soviets themselves did not pick up on Ufimtsev's research or other stealth designs, the answer is rather complicated. For one thing, the translating stealth theory into practical aircraft required advanced avionics and flight control systems. US aircraft manufacturing tended to prioritize bleeding edge technology and as such, the US did have a lead on the Soviets in avionics. Although this American lead would narrow throughout the late 1970s and 80s, the state of US avionics industry meant the US stealth program could proceed. Additionally, the Soviet design and procurement process had somewhat ossified by the 1970s with a nebulous relationship between the Soviet state and the various OKBs with the state delegating to the OKBs responsibility for certain types of aircraft (Mikoyan- fighters, Sukhoi- ground attack, Tupelev- bombers, and so on). These design bureaus had a good deal of heft within the Soviet planned economy and could stifle innovation in Soviet aerospace. Upstart or maverick designers could find themselves swallowed up into these existing OKBs or find themselves cut off from state funding. An example of the latter case was the supersonic Tsybin RSR's failure in the 1960s whre the existing OKBs, led by Tupolev, managed to get funding pulled for a promising supersonic bomber-reconnaissance design. Creating an in-house design group like the Skunkworks was thus much harder for the Soviet system to pull off in this environment.

This is not to say that the Soviets were completely in the dark about American low-observable developments. According to a declassified CIA memo , the Soviets were aware of this black program and received a lot of their information on US stealth from open source journalism, especially International Defense Review's Bill Sweetman, which the CIA calculated was cited in approximately 40% of Soviet publications on stealth. While the memo doesn't go into specifics and is redacted in parts, they note that open source reporting from trade journals got the contours of the US stealth programs correct and the Soviets appreciated that this was a far more reliable source than the New York Times. Although it might seem like a poor intelligence source, open-source articles in trade journals often featured informed educated guesswork, such as the type of engine used or the internal weapons' bay, that were subsequently proved correct.

There is some evidence that the Soviets were moving towards incorporating low-observable technology into their designs in the 1980s and 90s. Another declassified CIA report from 1983 indicated that while the Soviets did not have an equivalent black project for stealth aircraft, they were aware of this development and were beginning to form projects of their own. The CIA report contended that the Soviets were mostly focusing their current efforts on reducing RCS rather than producing a pure stealth design. Many of the designs tendered for the MFI (also sometimes called I-90 [fighter-90s]) program often incorporated low-observable features like canted tails and internal weapons' bays. Yakolev's MFI submission had canted intakes much like the F-22 while Mikoyan's 1.42/1.44 also had some low-observable elements incorporated into the design. Press materials for the forward swept wing Sukhoi S-37 stressed that the design incorporated radar absorbent materials that lowered the RCS. Sukhoi also had a stealthy bomber program, the T-60S, of which very little credible information has surfaced.

The problem for Soviet stealth was that the maturity of the technology coincided with the implosion of the Soviet economy. The post-USSR aviation forms found contracts drying up and funding in research shrunk to hitherto unprecedented levels. Claims on Soviet (now Russian) stealth developments became difficult to parse out from sales pitches from an ailing aerospace industry desperate to assert that it had not fallen behind Western aerospace.

Sources

Buttler, Tony, and Yefim Gordon. Soviet Secret Projects: Bombers Since 1945. Leicester: Midland, 2004.

_. Soviet Secret Projects: Fighters Since 1945. Leicester: Midland Counties, 2005.

Crickmore, Paul, and Alison Crickmore. Nighthawk: F-117 Stealth Fighter. Ann Arbor, MI: Lowe & B. Hould Pub, 2002.