The very hour that the United States entered World War II, Winston Churchill decided to invite himself to Washington, D.C.

On December 8, 1941, even as Franklin D. Roosevelt was delivering his “day of infamy” speech to Congress, the British prime minister resolved to sail across the Atlantic to fortify his nation’s most important alliance. “We could review the whole war plan in light of reality and new facts,” an eager Winston Churchill wrote to Roosevelt. After expressing concern about Churchill’s safety in the U-boat-filled ocean—a concern the prime minister waved off—FDR assented. “Delighted to have you here at the White House,” the president replied.

Two weeks after Pearl Harbor, Churchill arrived in Washington for a three-week stay at the White House. He celebrated Christmas 1941 with FDR and Eleanor Roosevelt. As December became January—75 years ago this month—the president and prime minister bonded over late-night drinking sessions that annoyed the First Lady, taxed White House staff and cemented the partnership that won the world war.

On the morning of December 22, the day of Churchill’s arrival, the chief White House butler, Alonzo Fields, walked into an argument between Franklin and Eleanor Roosevelt. “You should have told me!” Eleanor said, according to Doris Kearns Goodwin’s book No Ordinary Time. FDR had just told her that Churchill was arriving that night to stay for “a few days.”

Churchill, whose warship had just docked in Norfolk, Virginia after ten storm-tossed days at sea, was anxious to travel the 140 miles to Washington to see Roosevelt. They had met four months earlier, in Newfoundland, to draft the Atlantic Charter, a joint declaration of postwar goals, including self-government for all peoples. Both men had hoped it would convince the American people to join the war and ally with Britain, but public opinion in the U.S. did not change until Pearl Harbor.

The prime minister flew to Washington from Norfolk on a U.S. Navy plane, and the president greeted him at Washington National Airport. Churchill arrived at the White House wearing a double-breasted peacoat and a naval cap, carrying a walking stick mounted with a flashlight for London’s Blitz-driven blackouts, and chomping on a cigar. Accompanying Churchill that first day were British ambassador Lord Halifax, minister of supply Lord Beaverbrook, and Charles Wilson, Churchill's doctor.

Upstairs, the First Lady, putting the best face on her sudden hostess duties, invited the prime minister and his aides to have tea. That night, after a dinner for 20 where Roosevelt and Churchill traded stories and quips, a smaller cohort retired to the Blue Room upstairs to talk about the war.

Churchill turned the second-floor Rose Suite into a mini-headquarters for the British government, with messengers carrying documents to and from the embassy in red leather cases. In the Monroe Room, where the First Lady held her press conferences, he hung up enormous maps that tracked the war effort. They told a gloomy tale: Germany and Italy in control of Europe from the English Channel to the Black Sea, Hitler’s army besieging Leningrad, Japan sweeping through the Philippines and British Malaya and forcing Hong Kong’s surrender on Christmas Day. That made Roosevelt and Churchill’s summit doubly important: The Allies needed an immediate morale boost and a long-range plan to reverse the tide of fascism.

The 67-year-old prime minister proved an eccentric houseguest. “I must have a tumbler of sherry in my room before breakfast,” Churchill told Fields, the butler, “a couple of glasses of scotch and soda before lunch and French champagne, and 90-year-old brandy before I go to sleep at night.” For breakfast, he asked for fruit, orange juice, a pot of tea, “something hot” and “something cold,” which the White House kitchen translated to eggs, toast, bacon or ham, and two cold meats with English mustard.

White House staff often saw the prime minister in his nightclothes, a silk gown with a Chinese dragon on it and a one-piece romper suit. “We live here as a big family,” Churchill wrote to British Labor Party leader Clement Attlee in a telegraph, “in the greatest intimacy and informality.” One night, imagining himself as gallant as Sir Walter Raleigh spreading his cloak over dirty ground for Queen Elizabeth I, Churchill took hold of Roosevelt’s wheelchair and wheeled him into the White House dining room.

Churchill and Roosevelt ate lunch together every day. In mid-afternoon, Churchill would often suddenly declare, “I’ll be back,” then retreat for a two-hour nap. Daytime was a prelude to his deepest work hours, from dinner long into the night. He kept Roosevelt up until 2 or 3 a.m. drinking brandy, smoking cigars and ignoring Eleanor’s exasperated hints about sleep. “It was astonishing to me that anyone could smoke so much and drink so much and keep perfectly well,” she later wrote.

But FDR hit it off with Churchill. “The President did not share his wife’s shock, nor her barely concealed disapproval,” Nigel Hamilton wrote in The Mantle of Command: FDR at War, 1941-1942. “He liked eccentricity, which made people the more interesting.” Though amused by Churchill—“Winston is not Mid-Victorian—he is completely Victorian,” Roosevelt said—he also admired his courage. He brought Churchill along to his December 23 press conference with 100 American reporters, who cheered when the 5-foot-6 prime minister climbed onto his chair so they all could see him. He was “somewhat shorter than expected,” the New York Times reported, “but with confidence and determination written on the countenance so familiar to the world.”

On Christmas Eve, Churchill joined the president at the annual White House Christmas tree lighting, moved from Lafayette Park to the White House’s South Portico out of wartime caution. “Let the children have their night of fun and laughter,” Churchill told the 15,000 onlookers gathered beyond the fence. “Let us share to the full in their unstinted pleasure before we turn again to the stern tasks in the year that lies before us.”

After attending a Christmas Day service with Roosevelt at a nearby church, Churchill spent most of the holiday working nervously on the speech he would deliver the next day to a joint session of Congress. “The task which has been set is not above our strength,” Churchill declared in his speech. “Its pangs and trials are not beyond our endurance.”

Thrilled by his roaring reception by Congress, which he’d answered by flashing the V-for-victory sign, Churchill returned to the White House excited and relieved. Upstairs that night, Churchill watched The Maltese Falcon with Roosevelt and Canadian prime minister Mackenzie King, and declared that the ending, during which Humphrey Bogart’s Sam Spade gives up the femme fatale he loves to the police, reminded him of a sad case he’d overseen as British home secretary. That night in his suite, Churchill was struck by a pain in his chest and arm—a minor heart attack. His doctor, not wanting to alarm him, simply told him he’d been overtaxing himself. Churchill, undaunted, took a train trip to Ottawa and addressed the Canadian parliament on December 30, then returned to Washington to continue the summit.

On New Year’s Day 1942, Roosevelt and Churchill visited Mount Vernon to lay a wreath on George Washington’s tomb. That night, they gathered in the president’s study with diplomats from several Allied countries to sign a joint declaration that they would fight the Axis powers together, and that none would negotiate a separate peace. The pact included a historic new phrase: At Roosevelt’s suggestion, it was called “A Declaration by the United Nations.” According to aide Harry Hopkins, Roosevelt hit upon the name that morning and wheeled himself to Churchill’s suite, unannounced, to run it by the prime minister. Ignoring a clerk’s warning that Churchill was in the bath, Roosevelt asked him to open the door. He did, revealing Churchill standing naked on the bath mat. “Don’t mind me,” Roosevelt quipped.

After a five-day vacation in Florida, Churchill returned to Washington on January 10 to conclude the summit. His three-week visit was fruitful for the war effort. Churchill and Roosevelt agreed on several strategies that would end up making a difference for the Allies. Churchill learned to his relief that despite Americans’ impatience for revenge against the Japanese, Roosevelt still intended to defeat Germany first, as the two leaders had agreed in Newfoundland. They also agreed to invade North Africa later in 1942, a move that proved an effective prelude to the Allied landings in Italy and France. At Roosevelt’s insistence, Churchill agreed that a single command center in Washington and supreme Allied commanders in Europe and Asia would coordinate the war effort. The agreement deeply upset British military leaders, but Churchill headed off criticism by telegraphing to Attlee, the acting prime minister in his absence, that it was a done deal.

Churchill left for England on January 14, 1942, flying home via Bermuda. “His visit to the United States has marked a turning-point of the war,” enthused a Times of London editorial upon his return. “No praise can be too high for the far-sightedness and promptness of the decision to make it.”

All those late nights took a toll on Roosevelt and his exhausted staff. Hopkins, looking ashen, checked himself into the naval hospital to recover. But the bond between president and prime minister—the trust that would win the war—was forged. Roosevelt, in the now-quiet White House, found he missed Churchill’s company. He sent a message to him in London that foresaw how their friendship would resonate in history. “It is fun to be in same decade with you,” it read.