Operation Unthinkable: Churchill's Secret Plan to Attack Stalin

Drafted in the shadows near the end of the Second World War, Operation Unthinkable was a top-secret plan like no other. Concerned with the growing threat posed to Western Europe by the USSR, Churchill ordered the preparation of a contingency plan: attacking the Soviet Union. This classified plan entailed a course of action that may have changed the course of history if the Big Three had actually gone to war. The plan weighed Soviet numerical superiority against Western advantages in strategic bombing and naval power — and ultimately concluded that the odds were too long.

Growing Tensions Between the West and the Soviet Union

While not a traditional ally of the United States and Great Britain, the Soviet Union had for a few years enjoyed a great relationship with them due to the common threat of the Axis powers. In fact, it was in large part thanks to the massive American Lend-Lease program and British intelligence that the Soviets were able to defend their nation and launch a successful counterattack against Germany on the eastern front. However, as cordial as everything may have seemed on the surface, in the closing months of World War II it was becoming clear to every side that the war’s end would not simply bring an end to global tension, but rather open the door to a new era of rivalry and mistrust between the West and the USSR.

The greatest cause of this growing tension was the disagreement about how much of post-war Europe should be governed. Stalin had made it clear that he intended to maintain control over many of the countries in Eastern Europe, some of which had been recently liberated by the Red Army, and others that had been annexed in 1939 under the Molotov-Ribbentrop Pact, a deal which had essentially split the region up between the Soviet Union and Germany, back before they were enemies. But with Germany now out of the picture, the Soviet Union was by far the dominant regional power.

The West did not fancy the idea of their new geopolitical rival gaining so much land and population, and despite Stalin reassuring everyone that these nations would have their own free elections, it was obvious that they were all turning into Soviet satellite states. Of particular concern was Poland, whose initial invasion and annexation had brought Great Britain and France to war with Germany in 1939. Though the occupying Germans had now been kicked out, they had merely been replaced with occupying Soviet troops, and the Communist Party was already dominating local elections in the war-torn nation.

This was especially frustrating as Stalin had agreed at the Yalta Conference to hold free elections in liberated territories, but it was clear who was pulling the strings. There was also a fear that Stalin may outright attack the West. After all, at the time, he had yet to deploy the Red Army against Japan, and with the US heavily occupied fighting in the Pacific, he may have seen Western Europe as ripe for the taking.

Churchill Orders a Plan for War Against the Soviet Union

Looking at all of this, Churchill approached the Chiefs of Staff Committee and requested that they prepare an emergency plan for military action against Stalin, in a move that would “impose upon Russia the will of the United States and the British Empire. Even though ‘the will’ of these two countries may be defined as no more than a square deal for Poland, that does not necessarily limit the military commitment.” This was Operation Unthinkable — a new war.

And in an ideal world, it would last only a few weeks. After Germany’s surrender in May 1945, Soviet troops were stationed in a line that extended from eastern Germany in the north all the way to the edge of Yugoslavia on the Adriatic Sea in the south. Churchill envisioned an attack using British, American, and Polish soldiers, as well as German divisions created from reformed prisoners of war, to launch a surprise attack on Soviet positions near Dresden and quickly overrun the frontline before a proper response could be mustered.

The idea was that if they moved with enough speed, Stalin may choose to negotiate instead of retaliate — after all, it was not Soviet territory under attack, just occupied land. At a minimum, Poland could be liberated, but, if fortune smiled upon the advancing divisions, perhaps huge chunks of Eastern Europe could be as well. The original date for this hypothetical invasion was set at July 1, 1945.

The Military Calculus: Forces, Strengths, and Weaknesses

The timing might seem soon after Germany’s surrender, but the Soviet Union had been absolutely devastated by the Second World War, and it would be better to strike sooner rather than later, before they could fully recover. However, the biggest issue facing Operation Unthinkable was the fact that the United States might not have been able to contribute their full force. While the war with Germany was over, the war with Japan was still ongoing, and the Pacific Theatre was keeping much of America’s power tied up far from Europe.

A report given to Churchill stated that without the full commitment of the US, Britain’s odds looked “fanciful” against the monstrous Red Army. But the total absence of the US was a worst-case scenario. Military planners estimated that by July 1945, the Western Allies would be able to muster up around 80 infantry divisions and 23 armored divisions.

These would be pitted against an estimated 223 Soviet infantry divisions and 26 armored divisions, giving the USSR a ratio of nearly 3 to 1 in land-based strength. The odds looked a little better in the skies. While the Soviets did technically outnumber the West when it came to fighters and ground-attack aircraft, the Soviet Air Force had some key weaknesses.

They had only minimal experience facing high-altitude strategic bombers, which meant that the American Boeing B-29 Superfortress could be a serious game changer. Additionally, much of the Soviet Armed Forces relied on Western aid through the Lend-Lease program, and cutting this off had the potential to be disastrous for Stalin. Nearly half of the USSR’s aviation fuel was supplied by the United States, which could cripple their Air Force if the two went to war.

However, much of the Lend-Lease supplies included things like hundreds of thousands of jeeps and trucks, 14,000 aircraft, and 13,000 tanks — things that would stay in the hands of the Red Army even after the program had ended. Another place the West had the advantage was with their undisputed naval superiority. The Soviet Union’s navy was not very high on their list of priorities and would not rise to its well-known global prowess until years later in the Cold War.

The United States, however, had a gargantuan navy at the end of World War II, including many aircraft carriers, which the USSR had no experience battling. Complete dominance on the seas could give the West a much-needed advantage, especially in operations along the Baltic Sea.

Potential Outcomes: From Quick Liberation to World War III

While drawing up plans for Operation Unthinkable, a few potential outcomes were deemed the most likely. The first was a fairly successful one, in which the West was able to quickly liberate Poland and push the frontline to the east, securing not only Poland but also the Soviet-occupied zones in Germany. After this had been achieved, the next move would be the one that would decide the course of history: should the Allies consolidate their gains and secure the liberated territories, or should they keep pushing eastward?

It was expected that if the initial surprise attack had been successful enough, and if the Western divisions had the clear combat advantage, Stalin would back down and give up his control over the region. This was the desired outcome, as it would minimize further war while still putting the Soviet dictator in his place and set a precedent to prevent Stalin from expanding in the future. But that was a rather optimistic future.

If Stalin refused to back down and began launching counteroffensives, the West might decide to continue onward to outright defeat the USSR, pushing perhaps as far as Minsk or Kyiv in an attempt to ramp up the pressure. If this were to happen, it is easy to imagine a scenario in which total war erupts once again across Europe, as the Soviet Union resumes its mass mobilization of its republics, and puts up a fierce fight as the West commences the bombing of Soviet population centers like Moscow and St. Petersburg.

Critical targets in this war would be the industrial centers in the Ural Mountains and the oil fields of southern Russia and the Caucasus, similar to Germany’s goals a few years earlier when they launched Operation Barbarossa. Reaching deep into Soviet territory had failed Germany — held off in the south at Stalingrad and in the north at Moscow. The West might be more fortunate, though one can envision hundreds of thousands to millions of casualties in the following months.

One important note is that while at war with Germany, the USSR scrambled to relocate their industry to the safety of the east, slowing down manufacturing capabilities while the facilities were constructed. But that relocation was already finished, and a renewed war on the same front would no longer pose the same threat to Soviet factories. The true scale of this war, and the chances of Western success, would depend not only on the United States quickly wrapping things up with Japan, but also on securing more allies in the region.

One major player that could tip the scales was China, who, after finally getting rid of Japan, would hypothetically be able to launch an offensive into eastern Russia. With Stalin fighting a war on two fronts, defeat would be imminent. However, this is once again highly optimistic, as the Chinese Civil War was returning to full swing, meaning the Republic of China would not risk sending away much of their manpower for a war they were not even involved in.

Soviet Espionage and the Cambridge Five

Another problem with all of this planning is that it assumed a largely defensive posture from the Soviet Union. Stalin could easily stir up chaos by launching counteroffensives in critical areas, such as invading Greece or Norway, which would pull Allied manpower away from the main attack. And with his own oil fields in danger, Stalin may also choose to invade the oil-rich nations of the Middle East to secure much-needed resources.

Very quickly, this was shaping up to look less like a quick grab of Poland and more like World War III. But perhaps the worst outcome of all was the chance of utter failure from the very start. Despite the Allies having a good advantage in strategic bombing and naval assets, the majority of the war would be fought on land in Central Europe, which could allow the Soviets to utilize their advantage in manpower.

In this scenario, not only does the West fail to advance through the frontline, but the Soviets are able to successfully counterattack and capture even more of Europe, perhaps the rest of Germany or more. This nightmare scenario would be a catastrophic defeat on the battlefield and would instantly make an enemy out of Stalin, who was now confident in his strength over the Western powers. What’s worse is that, in hindsight, this total failure was quite likely, and it is all thanks to Soviet spies.

In June 1945, just a couple of weeks before the hypothetical starting date of Operation Unthinkable, Soviet commander Gregory Zhukov suddenly ordered all of his troops in Poland to regroup and assume defensive positions. Historian John Erickson speculated that this may have been the result of leaked intelligence through a group known as the Cambridge Five. The Cambridge Five was a ring of British citizens operating as Soviet spies, recruited during their time at Cambridge University, who had gone on to secure various positions in the British government and military.

Thousands of documents were leaked to the Soviet Union through these five, and while this spying did not have many direct consequences since the two sides never went to war, it is very possible that they caught wind of Operation Unthinkable and sent it to the KGB, which is why Zhukov suddenly ordered defensive positions in Poland. This would have completely negated the West’s element of surprise, one of the major advantages they were counting on in the opening days of the attack, likely dooming the operation from the minute it began.

The Plan Is Shelved and the Atomic Shadow

The Chief of Army Staff signed a report for Churchill that stated, “It would be beyond our power to win a quick but limited success and we would be committed to a protracted war against heavy odds.” Churchill’s plan to attack Stalin was shelved for good. The codename Operation Unthinkable was recycled to a new contingency plan, prepared in case Stalin instead made the first move and began advancing toward the Atlantic Ocean, though this plan was also tossed out once it became clear that Stalin had no intention of starting a war.

At the time, Stalin himself noted, “Neither we nor the Anglo-Americans can presently start a war … everyone’s fed up with war.” It is a very good thing that everyone was fed up with war, because if Operation Unthinkable did spiral into a third world war, it had the potential to become even deadlier than the first two. The United States would soon be in possession of atom bombs and would soon set a precedent by dropping them on Hiroshima and Nagasaki in the name of preventing an invasion of the Japanese mainland.

Because it is true that far more lives would have been lost had the US launched an all-out invasion of Japan, it is possible that the same logic could have been used against Stalin. Why fight a protracted war leading to the deaths of millions when a few atom bombs on Moscow, St. Petersburg, and Kyiv would end hostilities in an instant?

It is an alternate history that was truly unthinkable, and the plan was never pursued.