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Operation Unthinkable: Churchill‘s Daring Plan for War With the Soviet Union


As the Second World War drew to a close in Europe, the uneasy alliance between the Western powers and the Soviet Union began to unravel. Despite their common enemy in Nazi Germany, tensions were high between the erstwhile allies, particularly over the future of Central and Eastern Europe. It was in this context that British Prime Minister Winston Churchill conceived of one of the most audacious and controversial military plans in modern history: Operation Unthinkable, a surprise attack on the Soviet Union to be launched in the summer of 1945.

The Yalta Conference and the Postwar Divide

To understand the origins of Operation Unthinkable, we must first look back to the Yalta Conference of February 1945. At this pivotal meeting, Churchill, US President Franklin D. Roosevelt, and Soviet Premier Joseph Stalin gathered to hash out plans for the postwar order. While the leaders agreed on the need to divide Germany and hold free elections in liberated countries, there were signs of brewing discord.

Churchill, in particular, was wary of Stalin‘s intentions. The Soviet leader had already reneged on his promise to allow free elections in Poland, instead installing a communist government friendly to Moscow. As the Red Army swept across Eastern Europe, Churchill grew increasingly alarmed that the Soviets would soon dominate the entire region. "This war is not as in the past," he warned. "The whole map of Europe has been changed… And there is nothing I will not do to prevent another war."[^1]

The Plan Takes Shape

Motivated by these concerns, in May 1945, Churchill tasked the British Armed Forces with drafting a contingency plan for war with the Soviet Union. The resulting document, codenamed Operation Unthinkable, laid out a daring offensive aimed at pushing the Soviets back to Poland‘s pre-war borders and preventing the spread of communism in Europe.

The plan called for a massive attack along a 1,700-mile front stretching from the Baltic to the Adriatic. British and American forces, potentially supplemented by rearmed German units, would strike Soviet positions in Germany, Poland, Czechoslovakia, and the Balkans. The objective was to catch the Red Army off guard and drive them back east, establishing a buffer zone of friendly states between the USSR and Western Europe.[^2]

Allied army positions on 10 May 1945
_Allied army positions on 10 May 1945. Source: Wikimedia Commons_

Military Realities and Ethical Dilemmas

However, the planners tasked with assessing Unthinkable quickly realized the enormity of the challenge. The Red Army, battle-hardened after years of brutal fighting against the Wehrmacht, numbered over 6 million men in Europe alone. By comparison, the Western Allies could muster at most 1 million troops. Even with tactical surprise and air superiority, British commanders concluded that Unthinkable was likely to fail in its initial objectives.[^3]

Moreover, there were serious ethical concerns about the plan. The idea of rearming German soldiers, many of whom had just been defeated and some of whom were suspected of war crimes, was deeply troubling. As one British officer put it, "The idea of collaborating with Russians one day and fighting them the next, of arming Germans and instigating them to kill our present allies, seemed to me shocking."[^4]

The American Reaction and Churchill‘s Retreat

Despite these reservations, Churchill initially pressed ahead with the plan, hoping to convince the United States to support it. However, he found little enthusiasm in Washington. American leaders, focused on defeating Japan and wary of a new conflict, saw little strategic benefit in confronting the Soviets. President Harry Truman, who had succeeded Roosevelt after his death in April 1945, was particularly skeptical. "We‘ve got to have the Russians in the Japanese war," he told his advisers. "My objectives are to get the Japanese war won and to keep the Russians friendly."[^5]

Faced with American opposition and a change of government at home (Churchill‘s Conservatives were defeated by the Labour Party in July 1945), Operation Unthinkable was quietly shelved. By the time Churchill left office, the plan had been all but forgotten, its details hidden away in classified files.

The Iron Curtain Descends

Yet the tensions that had given rise to Unthinkable did not disappear. In a speech in Fulton, Missouri in March 1946, Churchill famously warned that an "iron curtain" had descended across Europe, dividing the continent into Soviet and Western spheres of influence. His words, delivered with Truman at his side, marked a rhetorical turning point in relations between the former allies.[^6]

Cartoon depicting Churchill's Iron Curtain speech
_Contemporary cartoon depicting Churchill‘s "Iron Curtain" speech. Source: Wikimedia Commons_

In the years that followed, both sides would develop extensive war plans targeting the other. The US Joint Chiefs of Staff drafted Operation Dropshot, a massive atomic bombing campaign against Soviet cities, while the Soviets prepared for a potential invasion of Western Europe. The world had entered a new era of superpower rivalry, one in which the threat of global annihilation was never far from leaders‘ minds.[^7]

Unthinkable‘s Legacy and Lessons

Operation Unthinkable was a product of its time, reflecting the deep mistrust and ideological divisions that emerged in the wake of World War II. It‘s tempting to dismiss the plan as a reckless gambit, one that could have plunged the world into an even more devastating conflict. Yet it also speaks to the difficult choices and moral compromises that leaders face in times of geopolitical upheaval.

In considering the use of force to shape the postwar order, Churchill and his military planners grappled with questions that still resonate today. What are the limits of diplomacy in dealing with authoritarian regimes? When is military action justified to prevent a perceived threat? And how can nations balance their ideological commitments with the pragmatic realities of power politics?

Ultimately, Operation Unthinkable serves as a case study in the risks and unintended consequences of preventive war. It‘s a reminder that even the most carefully laid plans can be overtaken by events, and that the line between deterrence and provocation is often perilously thin. As the world enters a new era of great power competition, with rising tensions between the US, China, and Russia, the lessons of this strange chapter in Cold War history are well worth heeding.

[^1]: Churchill to Foreign Secretary Anthony Eden, May 12, 1945, quoted in Reynolds, David. From World War to Cold War: Churchill, Roosevelt, and the International History of the 1940s. Oxford University Press, 2006, p. 249.
[^2]: British War Cabinet, "Operation Unthinkable," CAB 120/691, 22 May 1945, The National Archives, Kew, United Kingdom.
[^3]: Walker, Jonathan. Operation Unthinkable: The Third World War. The History Press, 2013, pp. 80-85.
[^4]: British officer quoted in Walker, p. 97.
[^5]: Truman quoted in McCullough, David. Truman. Simon & Schuster, 1992, p. 380.
[^6]: "The Sinews of Peace (‘Iron Curtain Speech‘)," The International Churchill Society, (accessed April 20, 2024).
[^7]: Ross, Steven T. American War Plans, 1945-1950. Routledge, 1996, pp. 11-15.