Following the end of the Second World War, relations between the Soviet and the Western Bloc deteriorated quickly. Former British Prime Minister Churchill claimed that the Soviet occupation of Eastern Europe after World War II amounted to 'an iron curtain has descended across the continent.' Relations were generally tense during the ensuing Cold War, typified by spying and other covert activities. The British and American Venona Project was established in 1942 for cryptanalysis of messages sent by Soviet intelligence. Soviet spies were later discovered in Britain, such as Kim Philby and the Cambridge Five spy ring, which was operating in England until 1963.