1934 – 1963
The Cambridge Five (Kim Philby, Guy Burgess, Anthony Blunt, John Cairncross, and Donald Maclean) were British civil servants who, unbeknownst to the British government, had become Communists while at university, and recruited as Soviet agents shortly thereafter. The spy ring was one of the most effective Soviet intelligence efforts of the Cold War, as all five rose to positions of great responsibility and trust in the civil service. Maclean, in particular, was privy to a large number of nuclear secrets; the information regarding the size and readiness of the Western nuclear arsenal played a key role in Stalin’s decisions to blockade Berlin and to arm the North Koreans for their invasion of South Korea. The spy ring fell apart when the U.S. VENONA project exposed Maclean; he and Burgess defected in 1951. Philby was able to elude exposure until 1963, passing secrets all the while; he too managed to defect. Blunt was unmasked around the same time, but secretly gave a confession, exposing other agents (including Cairncross).
Time: Early War
Removed after event: No
This is an event that is generally triggered only in the headline phase. It is a somewhat weak headline for the USSR only because the odds of success are usually low. Nevertheless, the payoff can be huge: not only can you combo it with an AR1 play to take over a battleground (a sort of USSR NORAD), you can also use it to gain access in a critical region that you are otherwise locked out of (like a mini De-Stalinization).
The Cambridge Five is best headlined on a turn that maximizes the odds of the US having a scoring card in hand: on Turn 3 or Turn 7, you may be able to positively identify a particular scoring card in the US hand if it hasn’t shown up yet in that reshuffle. Alternatively, it’s also a wise headline if it’s Turn 6 and few of the scoring cards have yet shown up in the Mid War reshuffle. It should go without saying that if the reverse is true (if all the scoring cards have come out already), then this is a null headline.
Note that if the US has multiple scoring cards, the USSR chooses one (and only one) of them to apply to the Cambridge Five.
Completely harmless, so long as you play it with no scoring cards left in your hand. It is ideally played at the end of your turn, as the knowledge that you have no more scoring cards can be advantageous to the USSR, but even if you have to play it earlier in the turn, it’s not really that bad of an event (because it does not expose the rest of your hand).