Reminder: Any CIA or MI6 agent who lasted more than a week in the Soviet Union had diplomatic cover. The NKVD and KGB caught all of our deep cover agents within days; in some cases within hours.
The United States excels at sigint and aerial/orbital recon, but the Russians have been top-notch at humint for a long time.
The United States excels at sigint and aerial/orbital recon, but the Russians have been top-notch at humint for a long time.