The White House alerted the press at 10:20 a.m. Sunday that Biden would not be seen for the rest of the day. In reality, he had not even been in the building for several hours.

Biden left his famous address at 1600 Pennsylvania Avenue even earlier that morning to fly to Poland. He then reportedly took a train to Kyiv, where he arrived early Sunday morning.

It was a surprise trip to the capital city of war-torn Ukraine roughly one year since Russian forces first launched an unprovoked invasion.

The president’s closely guarded travel was the product of months of planning that culminated with Biden standing side-by-side with Ukrainian President Volodymyr Zelensky and declaring the U.S. and the world would support Ukraine for as long as it takes to win the war.

“It was logistically complicated and difficult, and it sends an incredibly powerful message that President Biden has faith in the Ukrainian people and is unwavering in his commitment to stand by them,” White House communications director Kate Bedingfield said of the trip.

Biden’s trip to Ukraine was “meticulously planned over a period of months,” deputy national security adviser Jon Finer told reporters on Monday. A small number of officials from the National Security Council, the Pentagon, Secret Service and the White House military office were involved in the planning, he said.

The trip to Ukraine differed from past unannounced presidential visits to war zones like Iraq and Afghanistan because the U.S. does not have an established military presence on the ground there.

The president himself made the final decision on Friday to proceed with the trip to Kyiv ahead of a previously announced visit to Warsaw, which is roughly 500 miles from the Ukrainian capital.

“He got a full presentation of a very good and very effective operational security plan. He heard that presentation, he was satisfied that the risk was manageable, and he ultimately made the determination,” national security adviser Jake Sullivan told reporters.

Sullivan said the White House notified Russian officials of the impending trip to Ukraine before Biden departed, though he did not give an indication of how Moscow responded to the heads up.

Biden arrived at Joint Base Andrews and boarded Air Force One at 4 a.m. on Sunday, and the plane took off a short time later. After a refueling stop in Germany, Biden’s plane landed in Poland. The New York Times reported Biden traveled by train into Ukraine, arriving in Kyiv at roughly 8 a.m. local time on Monday.

The White House took significant steps to keep the trip under wraps until Biden arrived in Kyiv, and to ensure his security once he arrived. Officials had in recent days brushed aside questions about whether Biden would cross into Ukraine during his trip to Poland, saying there were no plans for the president to travel anywhere other than Warsaw.

Only three White House staff members traveled with Biden aboard Air Force One: Sullivan, deputy chief of staff Jen O’Malley Dillon and director of Oval Office Operations Annie Tomasini.

A 13-person press pool typically travels with the president, consisting of print, radio and broadcast reporters, as well as photographers and a videographer. Only two reporters traveled with Biden aboard Air Force One: a single print reporter, and a photographer, both of whom turned over their phones as a security precaution that is typical of unannounced presidential travel.

A two-person TV crew joined Biden’s motorcade upon his arrival in Kyiv, and nine more journalists were able to join for Biden’s meeting with Zelensky at the presidential palace.

While in Kyiv, reporters on the ground agreed not to share real-time updates on Biden’s movement and locations, and details on how he traveled to and from the city were withheld until he was out of the country. 

Biden spent roughly five hours in Kyiv, meeting with Zelensky, U.S. Ambassador to Ukraine Bridget Brink and other Ukrainian officials.

While there, Biden announced an additional $500 million in military aid for Ukraine and upcoming sanctions to further pressure companies and individuals supporting Russia’s war effort. More broadly, he spoke about the importance of the U.S. and its allies continuing their support for Ukraine after a year that saw thousands of Ukrainians lose their lives in a brutal war, themes he is expected to reiterate in a Tuesday address from Warsaw.

“One year later, Kyiv stands,” Biden said from the capital. “And Ukraine stands. Democracy stands.”