MI5 and Atomic Scientists (1945-1958): the Case of Patrick Blackett


At the Potsdam Conference (1945), President Truman informed the Soviet leader Stalin that the USA had recently tested the first atomic bomb. The ensuing droppings of this new, super-powerful weapon on Japan put a rapid end to the Second World War (WWII), establishing the United States as the dominant power. In the war’s direct aftermath, international tensions resulted in a strong dichotomy between two blocks: the free, democratic West led by the USA, and the Soviet-dominated, communist East, comprising the USSR and its Eastern European satellites. With geopolitical stakes revolving mainly around nuclear weapons’ development, the newly-founded United Nations almost immediately tried to enforce control over their proliferation. This attempt, made particularly difficult by diverging political agendas, eventually resulted in failure (Gowing, 1974).


Punch cartoon - The European hotch-potch (Shepard, 1945)

In such an explosive atmosphere, Attlee’s Labour government decided in 1947 to develop a nuclear bomb, hoping to insure Britain’s strong position as the second atomic power. The institutional machinery was however faced with fierce opposition, especially from those who could best understand the hazards of this nuclear policy – the scientists. In parallel, escalating cold-war anti-communist sentiments gradually increased the British government’s distrust of left-wing organisations, more specifically of left-wing nuclear scientists, as their political allegiances raised a fear of leakage to the Soviet Union (Deery, 2002). Britain’s Security Service MI5 therefore reinforced its investigation of such scientists (Andrew, 2010) – among them, one of the most-renowned was physicist Patrick M.S. Blackett. The recent declassification of the MI5’s Personal KV2-Files gives an opportunity to examine the Service’s assessments and to place them in their wider early Cold War context (1945-1958). This article will therefore focus on Blackett as a prominent dissenting figure in the corridors of power, demonstrating that his forceful, repeated, and red-tinged opposition to the government’s nuclear policies was what drew MI5’s attention to his activities from 1931 onwards.

Since his undergraduate years in Cambridge, Blackett held sympathies for leftist movements. Like many other distinguished scientists of his generation, he supported the ‘Scientists’ Popular Front’ that arose in Britaiin the 1930s (Melitz, 1959). Indeed, during the interwar period, the scientific community was regarded as socially unfit, leading its few politically active representatives to adopt a far-leftist, sometimes radical, stance. Science only interested the public at the dawn of WWII due to its significant contributions to the preparation for warfare. However, its misuse by fascist organisations across Europe for inhuman ends, such as eugenics, fuelled concerns about the social responsibility of science (Werskey, 1971), notably among members of the ‘visible college’ – Werskey’s name for the most significant group of left-wing scientists comprising the Scientist’s Popular, whose ideas Blackett undeniably shared (Werskey, 2007). ‘By the early thirties, their convictions – rekindled by the twin crises of Depression and Fascism and reworked through Soviet Communism and Marxist theory – led to a sustained burst of political action’ (Werskey, 2007, p.315).



Casing and assembly drawings of Fat Man (Los Alamos National Laboratory, 2020)

Throughout WWII, Blackett worked for the Navy and the Air Force, granting him access to secret military material. Hence when in 1935 Dobb, British economist and Soviet agent, suggested that Blackett, who travelled extensively to the USSR, ‘might become a member of the Editorial Board of a « Marxist Theoretical Journal »’ (1a, KV-2/3217, 1935), MI5 flagged Blackett as a person of interest (1a, KV-2/3217, 1935). Blackett was also later asked his views regarding Britain’s plan to acquire a fission bomb – the Tube Alloys Project. Given his serious criticism of the efficacy and morality of bombing policy in general, dating back to the failure of the 1942 bombing offensive against Germany, Blackett argued against Britain developing a bomb on its own (Nye, 2004).


This staunch opposition led to arguments with Churchill’s scientific adviser and maindefender of bombing policy Lindemann, who had already requested MI5 for an assessment of Blackett in 1941. However, MI5 asserted it was ‘very doubtful Blackett would be up to anything detrimental to this country’ (32a, KV-2/3217, 1941) considering he had already been in a position to pass secret information to the enemy, but no evidence of any positive connection with the Communist Party (CP) was ever uncovered (35a, KV-2/3217, 1943). Despite MI5’s reassurances that he was ‘entirely harmless from the political angle’ (35a, KV-2/3217, 1943), Blackett’s dissenting views earned him the long-lasting reputation of an outspoken sceptic and occasional defeatist.

Indeed, immediately after WWII, Blackett adopted an unpopular position towards nuclear policy on international and national levels. He argued that the bombings of Japan were unnecessary to ensure victory, but rather strategic acts to keep the USSR out of the Far East, as well as to justify the costs of the Manhattan Project (Hore, 2003). Thus, ‘the nuclear attacks were the beginning of the Cold War, not the end of the Second World War’ (Hore, 2003, p.203). In a widely-read pamphlet, Blackett also demonstrated with mathematical rigour the infeasibility of Washington’s Baruch Plan, that included freezing the development of atomic weapons rather than banning them; a reduction in conventional forces – ‘the one area of Soviet supremacy’; and the abolishment of veto by UN Security Council members (Jones, 1986, p.2). He concluded that since sanctions between equally powerful nations would be inapplicable, nuclear deterrence was largely overrated (Blackett, 1946).


Competing Cold War Perspectives (Unknown, n.d.)

Furthermore, the post-war American stance on nuclear cooperation put Britain’s atomic projects in a difficult position. Indeed, ‘Britain saw the bomb as a guarantee of a continued place in the inner circle of international diplomacy’, a means to ‘assert [its] independence of the US as well as to counter the USSR’ (Jones, 1986, p.3). However, the US, aiming to preserve their monopoly, instituted the McMahon Act (1946), forbidding the sharing of ‘information about nuclear technology with any other power’ (Ball, 1995, p.440). Therefore, Blackett increasingly voiced the opinion that the British government had become a puppet of the Americans’, advocating neutrality in Britain’s foreign policy (Nye, 2004, p.81). Despite his involvement in nationwide campaigns and his influential position in Attlee’s government, his attempts to prevent the proliferation of atomic weapons met with the British government’s indifference, which was, at the time, consciously removing the question of nuclear development from public debate (Jones, 1986, p.10).

Blackett’s strong links with the communist faction of the Association of Scientific Workers (AScW) were the earliest red flag for MI5. Moreover, in 1947, the Service noted that:


prior to the arrest in 1943 of David Springhall on charges under the Official Secrets Acts, Blackett had been giving «really first-rate information » to members of the Communist Party of Great Britain (CPGB). Although it is unclear whether Blackett stopped ‘through fear of discovery or because he had suddenly become aware of the possibility of its being misused’ (72a, KV 2/3217, 1947)

This action justified MI5 in obtaining a Home Office Warrant (HOW) to record all his telephone conversations; no useful information, however, ensued (108a, KV-2/3217, 1947). Nevertheless, the government’s high level of distrust in the CPGB, considered a 5th Column serving an ‘alien dictatorship’ (Deery, 2011, p.11), occasionally resulted in refusing permission for leading scientists like Blackett to visit Russia, provoking the scientific community’s ‘amazement and indignation’ (49b, KV-2/3217, 1945).



Socialism choking Britannia (Conservative Party, 1909)

In 1948, shortly before he was awarded the Nobel Prize, Blackett’s book generated a great controversy in Britain’s scientific as well as political circles. His conclusions on international control of atomic energy indeed ‘differ[ed] considerably both from the beliefs developed by American and British atomic scientists in 1944–45, and from the official positions of their respective countries’ (Shils et al., 1949, p.1). In his view, despite its power, the A-bomb could by no means replace conventional weapons, as nations would eventually run out of atomic resources. Thus, traditional armies would inevitably play a decisive role in the event of a nuclear war, dispelling the growing American fear that even they could be defeated in a few weeks by another atomic power. He even noted that such paranoia made the US more likely to use the bomb first as means of dissuasion than the USSR, still recovering from WWII (Hore, 2003).

In an ever-more polarised world, Blackett’s work ‘seemed to many to be inhumanly cold, perverse and probably communist’ (Hore, 2003, p.201), leading to his eventual exclusion from further governmental deliberation. Significantly, however, MI5 gave a much more objective assessment of his book: ‘it can’t be described in any way as propaganda for communism, it might be a little anti-American merely because the author is at pains to be fair to the USSR’ (274a, KV-2/3219, 1954). MI5’s main concern was that ‘his somewhat ingenuous attitude towards certain political problems raised a fear of leakage throughless scrupulous third parties’, thus concluding Blackett’s access to defence secrets would represent a risk, which ‘should be weighed against the positive advantages to be derived from his assistance’ (155a, KV-2/3218, 1949).



'We have now entered the Atomic Age' (Quade, 1952)

A chain of events further intensified international tensions. In mid-1949, the USSR shocked the West by successfully detonating an atom bomb about two years earlier than expected, putting them on an equal footing with the US. Four years earlier, Gouzenko’s defection, probably the most famous cipher clerk in the history of intelligence (Hennessy, 1984), exposed the existence of major home-grown spy rings. The Venona documents – the codename given to the Anglo-American decryption of Soviet wartime intelligence and diplomatic communications, led to the identification of German-born physicist Fuchs, responsible for the leakage (Hennessy, 1984). MI5 was granted a new HOW to ascertain Blackett’s reactions to his colleague’s arrest, which produced nothing of value, again (161a, KV-2/3218. 1950). Fuchs’ trial in early 1950 froze all UK-US negotiations to restore nuclear cooperation: it fuelled a paranoia across the Atlantic, leading to an intensification of the witch-hunts and increasing the American pressure for a tightening of British security procedures (Goodman, 2005). Unluckily for Britain’s interests, the first tripartite conference was held just prior to the invasion of South Korea. With the raging war in Vietnam and the Chinese Communist Revolution, Cold War seemed to be turning hot very rapidly. The second conference occurred just as Pontecorvo, another leading British scientist, unexpectedly defected to the SU, soon followed by diplomats Burgess and Mclean. The incoming Churchill administration was then forced to extend positive vetting to every person holding a vital post in government service’ (Hennessy, 1984).

By that time, however, MI5 noted that ‘Blackett seemed to have deliberately dissociated himself from extreme left- wing politics’ (206a, KV-2/3219, 1951), being even regarded ‘as a political traitor’ by the CPGB (221b, KV-2/3219, 1952). As to why he hired many communists on his staff when he moved to Imperial College in 1953, they suggested that he was probably too independent-minded to accept ‘the exclusion of communists from secret work merely because of their political creed’ (268a, KV-2/3219, 1954). So, despite his violent opposition to government policies, Blackett was considered such a loyal citizen that, in 1954, F-Branch assessed there would be ‘no substantial risk should [his] services be required in a connection which would afford him opportunity for subversive activities’ (270a, KV-2/3219, 1954).



The Russian Atomic Spy Ring (New York Times, 1951)

MI5’s evaluation radically changed in the mid-1950s. An extensive investigation indeed revealed Blackett’s close links with two Soviet Embassy officials identified as Intelligence Officers. Given the previous suspicions that he might have divulged secrets to the CPGB in the 1940s, these associations seemed more than dubious, especially for a man who displayed publicly the abandonment of his old allegiances (355a, KV-2/3220, 1957). Blackett was also described as a great enthusiast who could have disclosed ‘secrets purely on the spur of the moment’, as well as ‘brilliant megalomaniac’ (344a, KV-2/3220, 1957), playing the self-appointed role of mediator in international relations. Such an opinionated and unpredictable personage could therefore hardly be trusted with governmental secrets (338a, 343b & 402a, KV-2/3220, 1957-1959).

This appraisal notwithstanding, Blackett’s 1956 book was in fact much closer to the contemporary conventional wisdom. Reviewer Hodgson highlighted that ‘most of [his] conclusions [...] were first vigorously attacked and then quietly accepted’, even in the US (Hodgson, 1957, p.598).The 1954 Lucky Dragon incident had indeed reversed public opinion on nuclear issues, when the American test shot of an H-bomb about 1,000 times more powerful than the A-bombs dropped on Japan caused one of the worst radiological catastrophes in history (Jones, 1986, p.13). The decision for Britain to construct its own H-bomb regardless of the growing ethical controversy thus generated great criticism and the mass mobilsation of scientific associations from all political sides (Jones, 1986, p.15). World-famous scientists including Russel and Einstein further pressed for pacific solutions to international conflicts for the sake of survival. Simultaneously, the 1956 Soviet invasion of Hungary disheartened many British sympathisers, while the 1957 Sputnik satellite launch marked the beginning of the Space Race, forcing the government to reevaluate its position once again. Despite MI5’s concerns, Blackett’s conclusions then echoed those of the government’s Defence Paper (1958): the obvious technological gap doomed Britain to play the role of an ‘integrated’ power if the world was to remain nuclearised (Laucht, 2012).


Science Atomic Bomb Poster (vinter6700, n.d)

Such public approval contrasted sharply with the hostility his earlier works faced. Attlee’s Parliamentary Secretary Wilson later recalled that ‘his appointment of Blackett to the National Research and Development Corporation in 1949 [...] provoked one of the most violent political reactions in Parliament [he] had known in thirty years of Parliamentary turbulence’ (Nye, 1999, p.152). Blackett’s strong involvement in the affairs of state of his time, and his apparent determination to thwart governmental agendas were the main reason MI5 considered him a threat. The grounds on which Blackett was investigated by MI5 – his unequivocal socialist allegiances along with his unreserved criticism of nuclear policy, were more than reasonable. It is undeniable however, that the volatile context of the early Cold War when not fully supporting the West often meant to be against it, largely influenced Blackett’s pillorying as a prospective troublemaker (Nye, 1999, p.137). In this regard, MI5 appears to have remained impartial, arguing in favour of Blackett when questioning of his loyalty was at its peak; relaxing their distrust when he seemingly cut off all his communist links; and later expressing strong reservations in light of new incriminating evidence. However, as the analysis of the KV-files demonstrated, despite his polemical reputation and the intense suspicions that hung over him for at least the first two decades of the Cold War, MI5 failed to ever uncover any irrefutable evidence that Blackett was at any point, in fact, a Soviet agent.



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United Kingdom National Archives, Kew, (PMS Blackett) KV 2/3217 - KV 2/3220.

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