In the early days of the cold war, successes for the CIA were few and far between. The gradual Soviet takeover of Romania, the Soviet takeover of Czechoslovakia, the Soviet blockade of Berlin, CIA assessments of the Soviet atomic bomb project, the Korean War, and then, when the 300,000 Chinese troops waiting at the Korean border entered the war, all, arguably, failures of Central intelligence of the highest profile imaginable. The famous double agent Kim Philby was the British liaison to American Central Intelligence. Through him the CIA coordinated hundreds of airdrop operations inside the iron curtain, all compromised by Philby. American intelligence suffered from almost countless compromises of the networks it tried to set up. There were spies in the Manhattan project, and even Arlington Hall, the nerve center of CIA cryptanalysis was compromised by William Weisband, a Russian translator and Soviet spy. The CIA reused the tactic of dropping plant agents behind enemy lines by parachute again on China, and North Korea. This too was fruitless.