In 1961, Kisevalter was assigned to handle another GRU member, Colonel Oleg Penkovsky, who had also volunteered to spy. For almost two years Kisevalter and the British Secret Intelligence Service (MI-6) jointly handled Penkovsky, who provided them with vital information on Soviet missile capabilities. Penkovsky's information was critical to the resolution of the Cuban Missile Crisis. In October 1962, Penkovsky and his British courier, Greville Wynne, were arrested by the Soviet KGB and convicted of espionage. Penkovsky was executed in 1963.