Penkovsky first offered his services as a double agent to the U.S. Central Intelligence Agency (CIA) in August 1960 but received a less-than-enthusiastic response. He then turned to Britain. An initial contact with Greville Wynne, a British businessman with a tangential relationship with MI6, led to Penkovsky's delivery of a packet of secret Soviet material in April 1961, the contents of which were shared with the CIA. The CIA and MI6 then agreed to jointly approach Penkovsky when he arrived in London on 20 April 1961 as head of a Soviet trade delegation. From that point on, he provided secret material either via Wynne, when visiting the West as a member of a Soviet trade group, or on park benches in Moscow to Janet Chisholm, wife of undercover MI6 officer Rodrick Chisholm. Soon Penkovsky was passing on a large amount of highly classified information.
Data on Soviet missile production provided by Penkovsky gave the West a realistic evaluation of the true strength of Soviet missile forces and revealed as illusory the so-called missile gap between the United States and the Soviet Union. The information was unambiguous; the United States was far ahead. Information provided by Penkovsky assisted greatly in verification in September 1962 when U-2 reconnaissance aircraft detected missile site construction in Cuba. Penkovsky's material helped President John F. Kennedy in dealing with Khrushchev and bringing about the removal of Soviet missiles from Cuba.
On 22 October 1962 Penkovsky was arrested by the Komitet Gosudarstvennoi Bezopasnosti (KGB) and confessed to his spying activities. He was tried, found guilty, and executed in Moscow on 16 May 1963. Wynne was seized a few weeks later. Imprisoned, he was exchanged in April 1964 for Gordon Lonsdale, a Soviet double agent then being held in a British prison. How Penkovsky was detected remains a mystery. He may have been discovered with Janet Chisholm during routine surveillance. He may have been betrayed by a double agent. Some have also suggested that Penkovsky was simply too careless. Nevertheless, most espionage experts consider him the most important Soviet spy for the West in the Cold War era.
Penkovsky, Oleg. The Penkovsky Papers. Garden City, NY: Doubleday, 1965.; Schecter, Jerrold L., and Peter S. Deriabin. The Spy Who Saved the World. New York: Scribner, 1992.