As we all know, Communism does a poor job at producing technology.
bttt
To read about how the Soviets acquired the F-111 capsule and the possible fate of the crew:
http://www.dtic.mil/dpmo/sovietunion/vietnam_working.htm
www.f-111.net/downloads/Moscow-Module.doc
http://www.dtic.mil/dpmo/sovietunion/0104_usrjc_apr_rpt.htm
Regarding Russians and technology stolen, bought, or acquired by war:
During the Vietnam War, the GRU tasked military industrial scientists and researchers with obtaining US military hardware and technology. This team of personnel was known as the "special group" - they would try to gain access, via the North Vietnamese, to crash sites of US aircraft. In declassified Russian reports this team made complaints about the Vietnamese playing favorites with the Chinese (reports stated that by the time they arrived at a crash site, the site had been picked apart). These reports are genuine - they were written at a time when the Sovs would never imagine that such reports would be provided to the US.
The special group also could not travel without Vietnamese escort because they were white and could be mistaken for downed American pilots (which happened on a few occasions).
The North Vietnamese did a very good job of playing the Soviets off of the Chinese. This was at a time when the Chinese and the Soviets did not have a good relationship.
Soviet military officers mainly were assigned to Vietnam as Air Defense Advisors (at SA-2 regiments), mine-defusing teams from the Navy (at Haiphong), radio-technical engineers, AF advisors (but did not fly against the US pilots). Soviet AD advisors assisted the Vietnamese in shooting down our planes with the SA-2 system. However, the majority of our aircraft were downed by AAA (Anti-Aircraft Arty) - our pilots were quite adept at avoiding SAMs - to do so required low-level flying and that's where AAA is most deadly.