Detection
Maclean had little access to messages between Winston Churchill and Franklin D. Roosevelt, which usually bypassed both the State Department and the Foreign Office. Only one such message was discovered in Venona, which was a summary of Churchill's views on Eastern Europe to be put to Roosevelt by the British ambassador, Lord Halifax. Stalin always gave the impression of being already aware of information given to him by the Prime Minister and President at the 1943 Tehran Conference, the Yalta Conference in early 1945, and the mid-1945 Potsdam Conference. He showed no surprise when told that America would drop a bomb of enormous power on Japan, because he had been aware of the work of the Manhattan project for several years at that point, thanks to the work of atomic espionage agents.
Most of Maclean's cables published by the US Government in 1999 deal with routine messages between Lord Halifax, British ambassador in Washington and the Foreign Office in London or copies of reports from the British ambassador in Moscow Sir Archibald Clark-Kerr to London. Often they seem to have been drafted by the Foreign Secretary Sir Anthony Eden on behalf of Winston Churchill and voiced concern about Soviet political maneuvers in Poland and Romania. Churchill was trying to coordinate an Allied response to Stalin's imposition of rigid Soviet control. But Roosevelt showed no interest in blocking Stalin's moves in liberated Eastern Europe.
Maclean's role was discovered when the code name GOMER (Russian for HOMER) was discovered in the VENONA decryption carried out at Arlington Hall, Virginia and Eastcote in London between 1945 and 1951. These related to coded messages between New York, Washington and Moscow for which Soviet code clerks had re-used one-time pads. The full Venona transcripts were published in 1996 and show a resume of one cable from Churchill related by Maclean, during 1944 and 1945. In 1949, Robert Lamphere, FBI agent in charge of Russian espionage, along with cryptanalysts working as part of the Venona project, discovered that twelve coded cables had been sent, six from New York from June to September 1944 and six from Washington in April 1945, by an agent named Gomer, Russian for "Homer". The first cable sent but not the first to be deciphered described a meeting with Sergei on June 25 and Gommer's (sic) forthcoming trip to Tyre (New York) where his wife was living with her mother awaiting the birth of a child. This was decoded in April 1951. A short list of nine men was identified as possible Homers, one of whom was Maclean.
The second cable on August 2–3, 1944 was a description, but not a transcript, of a message from Churchill (Boar) to Roosevelt (Captain), which Homer claimed to have decrypted. It suggested that Churchill was trying to persuade Roosevelt to abandon plans for operation Anvil, the invasion of Provence, in favour of an attack through Venice and Trieste into Austria. This was typical of Churchill's strategic thinking since he was always looking for a flanking move. But it was rejected outright by both American and British generals.
Shortly after Lamphere's investigation began, Kim Philby, another member of the Cambridge Five, was assigned to Washington, serving as Britain's CIA-FBI-NSA liaison. He saw the Venona material, and recognized that Maclean was Homer, which was confirmed by his KGB control. He knew that some of the encoded messages KGB had been sent from New York, which Maclean had often visited to see his family, who stayed there with Melinda's mother.
The pressure on Philby now began to grow. If Maclean admitted sending messages, others of the Cambridge Five would be implicated. Philby had known Maclean at Cambridge and traveled to Moscow with him before the war for a holiday. Believing that Maclean would confess to MI5, Philby and Guy Burgess decided that Burgess would travel to London on the Queen Mary, where Maclean was head of the Foreign Office's American desk, to warn him. Burgess received three speeding tickets in a single day and assaulted a traffic cop in Virginia. The Governor complained to the British Ambassador and Burgess went back to London, in disgrace.
Philby passed this information to the Soviets, and they were desperate for Maclean to get out, fearful that, in his current state, he would crack immediately under interrogation. Maclean shilly shallied, afraid of staying, afraid of going, until he sounded out Melinda about the defection. According to Modin, she responded: "They're quite right - go as soon as you can, don't waste a single moment."
In common with many others, Cyril Connolly was reluctant to accept that Burgess and Maclean had spied for the Soviet Union: "they are members of the governing class, of the high bureaucracy, the “they” who rule the “we”…. If traitors they be, then they are traitors to themselves." he wrote later.
Read more about this topic: Donald Maclean (spy)