“If the Western Allies could inflict a rapid and crushing defeat on the Red Army, then Stalin would be forced to rethink his planned domination of Eastern Europe.”

By Giles Milton

AS STALIN’S Red Army fought its way towards the Berlin Reichstag at the end of April 1945, a bizarre rumour began spreading through the city’s underground shelters. The tale, if true, was sensational.

As one Berliner put it: “The Yanks and Tommies have quarrelled with Ivan [the Russians] and are thinking of joining with us [the Germans].”

Could it be true? Could the Western Allies really be contemplating an attack on Soviet forces to drive them out of Germany?

“No one knew what to believe,” that same Berliner recalled.

It would later transpire that these rumours were true – that is, they contained a grain of truth.

As the Red Army tightened its control over Berlin in the first week of May, British prime minister Winston Churchill ordered his Joint Planning Staff at the War Office to map out a massive ground, air and naval offensive against Soviet forces.

Churchill had long held that Stalin represented the greatest threat to the security of post-war Europe, despite having toasted him as “a friend whom we can trust” at the Yalta Conference less than three months earlier.

The fact that the Soviet leader was reneging on so many of the agreements struck at the summit, most notably the promise to hold free and fair elections in Poland, was vindication of Churchill’s belief.

If the Western Allies could inflict a rapid and crushing defeat on the Red Army, then Stalin would be forced to rethink his planned domination of Eastern Europe.

Operation Unthinkable was conceived as a military thrust deep into the heart of Soviet-occupied Europe, with the aim of imposing upon Russia “the will of the United States and British Empire,” as stated in a report from British military leaders to the prime minister.

Churchill’s call for a plan marked a dramatic escalation of his long-held hatred of Moscow’s Communist government. Ever since the Russian Revolution of 1917, he had sought to deal the Soviet regime a crushing blow. In 1919, he had sent British forces to Russia in order to aid the White armies doing battle with Lenin’s Bolsheviks. He described the Communists as “a league of failures, the criminals, the morbid, the deranged and the distraught,” while those who supported them were “typhus-bearing vermin.”

The war against Hitler had however led Churchill into an unwelcome but pragmatic alliance with Stalin. Now that the victory over the Third Reich as at hand, the prime minister reverted to his belief that the Soviet Union was the principal enemy.

The strategic architect of his proposed land offensive was Brigadier Geoffrey Thompson, an ex-commander of the Royal Artillery with professional expertise in the terrain of Eastern Europe. His battle-plan envisaged a massive drive east from western Germany towards Berlin and beyond. In all, 47 British and American divisions would push the Red Army back to the Oder and Neisse rivers, some 55 miles to the east of Berlin. This was to be followed by a climactic battle in the countryside around Schneidemühl (now Pila, in northwest Poland).

An armoured clash on a massive scale was expected, far larger than the battle of Kursk where 6,000 tanks had fought in the summer of 1943. Operation Unthinkable was to involve more than 8,000 tanks and would use American, British, Canadian and Polish forces. In the words of the brigadier: “We should be staking everything upon one great battle in which we should be facing very heavy odds.”

The odds were indeed heavy. The Soviets had 170 divisions available that spring, whereas the Western Allies had just 47 divisions. Thompson reckoned that the defeat of the Red Army would require the use of additional forces and he knew exactly where to find them. He proposed rearming the Wehrmacht and SS and using them to fight alongside the Allies. This would add another 10 divisions to the western army, with all of them hardened by six years of warfare.

This is where his plan came unstuck. Churchill’s chief military advisor, General Hastings Ismay, was horrified by the idea of allying with the remnants of Hitler’s armies and said that such a policy would be “absolutely impossible for the leaders of democratic countries even to contemplate.” He reminded Thompson that the government had spent the last five years telling the British public that the Russians “had done the lion’s share of the fighting and endured untold suffering.” To attack these erstwhile allies so soon after the end of the war would be “catastrophic” for public morale.

The distinguished field marshal, Sir Alan Brooke, was equally appalled and considered the brigadier’s offensive to be an act of supreme folly.

“Our view is that once hostilities began, it would be beyond our power to win a quick but limited success and we should be committed to a protracted war against heavy odds,” he wrote on behalf of the Chiefs of Staff. “These odds, moreover, would become fanciful if the Americans grew weary and indifferent and began to be drawn away by the magnet of the Pacific war.” Brooke concluded that “the chance of success [is] quite impossible.”

Whether or not the Americans were consulted is nowhere recorded, although General Patton is on record as saying that the Allies had a moral obligation to support the countries being swallowed up by Stalin.

“Day after day some poor bloody Czech or Austrian or Hungarian, even German officers, come into my headquarters with tears in their eyes they say, ‘In the name of God, General, come with your army the rest of the way into our country. Give us a chance to set up our own governments. Give us this last chance to live before it’s too late – before the Russians make us slaves forever.”’

If U.S. president Franklin D. Roosevelt had lived beyond April 1945, he too would have been appalled by the very idea of Operation Unthinkable. Determined to retain a good working relationship with Stalin, he had spent his dying months selling his idea of a new global body, the United Nations.

The hostility of Britain’s Chiefs of Staff would eventually kill off Operation Unthinkable, with them officially rejecting the plan on June, 8 1945.

Churchill regretted their decision, telling his foreign secretary, Anthony Eden, that if Stalin’s territorial ambitions were not dealt a definitive blow “before the U.S. armies withdraw from Europe and the Western world folds up its war machines, there is very little prospect of preventing a Third World War.” He also warned that the Red Army would soon be an invincible force.

“At any time that it took their fancy, they could march across the rest of Europe and drive us back into our island,” he warned.

But Churchill’s senior generals wanted nothing more to do with Operation Unthinkable. They enclosed the strategic plan in a grey government-issue folder marked Russia: Threat to Western Civilisation, along with its accompanying charts, tables and statistics. It remains in that folder to this day, housed in Britain’s National Archives under the shelfmark CAB 120/691. Each page is stamped in red ink with the words “Top Secret.”

Giles Milton is the author of Checkmate in Berlin: The Cold War Showdown That Shaped the Modern World. An internationally bestselling author of a dozen works of narrative history, including Soldier, Sailor, Frogman, Spy, Airman, Gangster, Kill or Die: How the Allies Won on D-Day. His previous work, Churchill’s Ministry of Ungentlemanly Warfare, is currently being developed into a major TV series. He lives in London and Burgundy. You can follow him on Twitter @GilesMilton1 or visit his website gilesmilton.com.