Among the most notorious atomic spies - Klaus Fuchs, Ethel and Julius Rosenberg, and Alan Nunn May - one name is often forgotten: Britain’s Donald Maclean, one of the Cambridge Five spies who undermined the Manhattan Project.
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US confidence in British intelligence nosedived during the Cold War after a ring of Cambridge University-educated spies working for the British government smuggled intelligence to the KGB.

Among the most notorious of the traitors was Donald Maclean, a British diplomat and intelligence officer who disappeared in 1951 along with a fellow operative, Guy Burgess. Both resurfaced in Moscow. They were described as hopeless drunks, unstable and promiscuous characters who’d been appointed to top jobs in London and at the British Embassy in Washington, D.C., and the US was livid.

The Americans pointed out that drunkenness, recurrent nervous breakdowns, sexual ‘deviations’, and other human frailties were considered security hazards and dismissible offenses in the US. Furthermore, Washington told London to “clean house regardless of who may be hurt”, according to declassified papers released by Britain’s National Archives.

The international incident had “severely shaken” the US State Department's confidence in the integrity of officials of Britain’s Foreign Office, the British Embassy reported back to the UK. 
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How to turn a British spy

Donald Maclean was born in 1913. His father, Sir Donald Maclean, was a Liberal Party MP and Opposition Leader from 1918 to 1920 so Maclean had a privileged upbringing and was educated at Cambridge University where he became a committed communist. There are differing reports about how Maclean was approached to spy for Moscow.

In Kim Philby’s confession, released by the British government, Philby says he supplied his handler “Otto” (later known as Arnold Deutsch) with a list of Cambridge University communist contacts.

Otto later turned up with a man introduced as 'Big Bill' who zeroed in on Donald Maclean and dismissed suggestions that Guy Burgess was unreliable and indiscreet. When Philby approached Maclean, Kim said his friend agreed at once.

Maclean, codenamed ‘Orphan’, became an agent of the NKVD, which later morphed into the KGB. He joined Britain’s Foreign Office and was soon handing over so many classified documents Deutsch told Maclean to slow down. 

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Don Maclean: all in the family

Maclean married his wife, Melinda, in 1940, and to the outside world they were the epitome of domestic bliss. Internally, trouble was brewing. Although Melinda initially claimed she was unaware of her husband’s activities, it later transpired that he’d revealed early on that he was a Soviet spy.

There were also early signs of instability. Maclean appeared to have a self-destructive streak and engaged in legendary drunken benders. During one such outing with friends in Egypt, Maclean was imbibing a lethal combination of whisky and Zebib, an Egyptian version of Arak. While the rest of the group watched, Maclean put his hands around his wife Melinda’s neck - as if to throttle her - then grabbed the rifle of an armed guard and beat him with it, according to Roland Philipps, author of A Spy Named Orphan. Maclean was tackled to the floor by the first secretary at the British Embassy who sustained a double fracture of his ankle. Maclean offered the injured man gin as an anesthetic.

Despite his antics, Maclean was a competent double agent, leaking thousands of classified documents to his Russian handlers from the start of his recruitment in 1934. During World War II, Maclean worked for the British Foreign Office and, between 1941 and 1945, he passed more than 5,000 documents to the USSR including high-level details of the atomic bomb project. 

Donald Maclean: atomic spy

Maclean was sharing information about uranium with Moscow in the early days of WWII, so he was up to speed on its usage and importance, Philipps writes. "He had been cited in Moscow as the source of a most secret report of the Government Committee on the development of uranium atomic energy to produce explosive material which was submitted on 24th September 1941 to the War Cabinet," Philipps added. Maclean also disclosed that General Leslie Groves and his Manhattan Project scientists planned to use 600 tons of uranium a year, which meant there was an acceleration in output rather than a slowdown.

Maclean was later posted to the British Embassy in Washington DC, between 1944 and 1948 - promoted twice, to Second Secretary, then First Secretary - where he had even better access to top-secret information on the development of atomic weapons and the Manhattan Project’s progress. The most dramatic and critical piece of information, according to Philipps, was that the Americans were far less successful in their work than expected. Operation Pincher, a 1945-50 US war plan, assumed 50 bombs would be ready within a year but by 1948 only a dozen were available. No more than 27 B-29 bombers had been modified to deliver those bombs - and even those were out of the range of the Soviet Union and based only in Britain and the Cairo-Suez region.

Some historians believe Stalin favored North Korea during the Korean War - and put the Berlin Blockade of 1948 in place - because he was relying on Maclean’s intel that America was not yet the nuclear power it claimed to be. Even as Truman announced on June 28, 1948 that the US was sending 60 'atomic capable' B-29 bombers to England and Germany, “Stalin knew from Maclean's earlier intelligence that they had only half the bombs and three assembly teams to arm these planes," Philipps writes.

Maclean was also able to keep the Soviets in the loop about British-American relations, including a summit between President Harry S. Truman and Prime Minister Clement Atlee that involved the founding of NATO.

“Maclean was considered to be an exceptionally hard worker at the embassy, his fellow diplomat Robert Cecil recalled: "He gained the reputation of one who would always take over a tangled skein from a colleague who was sick, or going on leave, or simply less zealous. In this way, he was able to maneuver himself into the hidden places that were of the most interest to the NKVD.”

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The end game 

By the late 1940s, Maclean’s drunken antics were becoming more noticeable yet he was promoted and made head of the American Department in the Foreign Office in London. The net was closing in, however. 

The Venona decryption project was carried out at Arlington Hall, Virginia and in London between 1945 and 1951 which related to deciphering coded messages sent between New York, Washington and Moscow. Maclean was about to be unmasked as a Soviet spy.

Kim Philby, by then based in Washington with Guy Burgess, apparently tipped off both men about the Venona investigation and plans were made for Maclean and Burgess to decamp to Moscow in 1951 on Maclean’s 38th birthday. Melinda Maclean and their children joined Maclean in Moscow more than a year after his defection but it would be five years before Khrushchev confirmed Maclean and Burgess were in the Soviet Union.

Maclean studied Russian, earned a doctorate, taught international relations, and served as a specialist on the economic policy of the West and British foreign affairs while living in Moscow until his death in 1983. 

His defection and spying remain a controversial and fascinating topic decades later. Maclean’s betrayal was a major blow to British intelligence at a critical time in history and the Cambridge Five spy ring - which included Maclean, Burgess, Philby, Anthony Blunt, and John Cairncross - is still considered one of the most damaging espionage operations in British history.