Almost as soon as World War II ended, the question of what to do with a defeated, destroyed Germany threatened to drive a wedge between the Soviet Union and the Western Allies. At Potsdam in 1945, the Big Three (the United States, Great Britain and the Soviet Union) agreed to divide Germany into occupation zones, with the Soviets taking the eastern half of the country and the United States, Great Britain and France dividing up the west. The capital city of Berlin, located deep within East Germany, was partitioned in much the same way.

Three years later, as the two sides found themselves increasingly at odds, the future of West Berlin hung in the balance. On June 24, 1948, outraged by the currency reform introduced by the United States and Britain into their occupied zones of Germany, the Soviets blocked all road, rail and water routes to the Allied-controlled sectors of Berlin. The blockade cut off the city’s electricity, food and coal supply, as well as its access to the outside world. For the Allies, coming to the aid of West Berlin—a democratic island in the middle of a communist state—was non-negotiable.

According to agreements made in 1945, the United States and Britain still had three air corridors to Berlin open to them, so they decided to airlift food, coal and other crucial supplies into the city from Allied military air bases in western Germany. On June 26, the United States launched “Operation Vittles;” Britain followed two days later with “Operation Plainfare.”

Over the next 11 months, American and British pilots ferried some 2.3 million tons of supplies into West Berlin on a total of 277,500 flights, in what would be the largest air relief operation in history. Though it began slowly, the Berlin Airlift grew more and more efficient. At its height, in the spring of 1949, an Allied aircraft landed at Berlin’s Tempelhof Airport every 45 seconds. The planes carried everything from food stuffs and medical supplies to coal and machinery, all vital to the survival of West Berliners who were hungry, scared and still reeling from the wounds inflicted during World War II. One of the airlift’s best-known heroes, U.S. pilot Gail S. Halvorsen, dropped parcels of candy, chewing gum and other sweets for the city’s children, earning the nickname “Candy Bomber.”

“The airlift was a lifeline for West Berlin,” says Hope Harrison, an associate professor of history and international affairs at George Washington University who has written extensively on the Cold War, Germany and Russia. “To feel that the U.S. and Great Britain, who had been their enemies, weren’t giving up on them. The last time they were doing anything, they were dropping bombs, and instead they’re bringing in food and coal and everything else.”

Though neither the Brits nor the Americans wanted war with the Soviets, they desperately wanted to maintain a Western presence in Berlin. As General Lucius Clay, the administration of US-occupied Germany, reported to Washington in mid-June 1948: “We are convinced that our remaining in Berlin is essential to our prestige in Germany and in Europe. Whether for good or bad, it has become a symbol of the American intent.”

The Allies reasoned that if the Soviets opposed the Berlin Airlift with force, they would be acting aggressively against a humanitarian mission and violating an explicit agreement. Though the Soviets did harass some Allied planes during the airlift, they didn’t take more aggressive steps against it, not wanting to risk all-out war with the West. Though the United States hoped to resolve the crisis peacefully, President Harry S. Truman’s administration did send B-29 bombers capable of carrying nuclear weapons to Britain during the airlift, indicating just how serious the situation had become.

“This was the biggest conflict yet in the developing Cold War,” Harrison says. “It made it absolutely clear—communists on one side, democrats on the other. It really made that clear to the Germans.” The airlift also convinced the French, she says, who had initially taken a more vindictive stance toward the German people after the war ended. “It took the blockade of Berlin to persuade the French, the new enemy is the Soviets. It’s not the Germans anymore,” Harrison explains. “It brought the French along with the U.S. and Brits to say, ‘Look, we’ve now got to help the Germans, because we have a bigger enemy.’”

On May 12, 1949, the Soviets ended the blockade of Allied-occupied Berlin after 11 months, and West Berliners began welcoming the first British and American land convoys. A few weeks earlier, the Western Allies had met in Washington to form the North Atlantic Treaty Organization (NATO), and two weeks after the blockade was lifted, the Federal Republic of Germany (West Germany) was formally established. “Stalin got exactly the opposite of what he wanted,” Harrison says. “He was essentially, with the blockade, trying to stop the creation of a West German state. Well, he got the creation of a West German state, and a Western military alliance.”

Early in the airlift, when British and American planes were struggling to carry the necessary amount of cargo to West Berlin, the Soviets offered to lift the blockade if the Allies withdrew the new Deutschmark from the city. But the Allies refused, and in the fall of 1948 some 300,000 West Berliners gathered at the Reichstag to show their opposition to Soviet domination, helping to convince the Allies to continue the airlift.

By the following spring, it was clear that the Berlin Airlift had become a massive success. Meanwhile, the Allied counterblockade that stopped all rail traffic into East Germany from the U.S. and British zones had dried up the region’s supply of coal and steel, hampering its industrial development and making the Soviets worry about a political backlash.

In October 1949, the German Democratic Republic (East Germany) was officially announced. Three years later, Stalin’s Soviet regime sealed the border between East and West Germany, leaving Berlin as the only conduit for East Germans looking to escape communism. Between 1949 and 1961, some 2.5 million of them fled via West Berlin, until in August 1961 the East German government erected the barbed wire fence that would become the Berlin Wall.

The crisis over Berlin in 1948-49 had cemented the division of Europe into communist and anti-communist states, and transformed the German capital, previously identified with Nazism and Hitler, into a Cold War era symbol of democracy and freedom. For West Germans, the Berlin Airlift would instill an enduring sense of gratitude toward the United States and Britain, their former enemies who had refused to allow them to be swallowed up into the communist regime, and had helped them when they needed it most.

Decades later, long after the Cold War faded into memory, the long-term effects of the Berlin Airlift lingered. “So many Berliners of that generation to this day have cans of food or powdered milk they kept as a souvenir [of the airlift],” Harrison says. “After the terrorist attacks of 2001 on the United States, the city of Berlin took out a full-page ad in the New York Times with pictures of the airlift. It said ‘You helped us in our hour of need—we will help you now.’”