The president stood solemnly and saluted the remains of civilian Scott A. Wirtz of St. Louis as they were carried from a C-17 military aircraft into a waiting van. Wirtz had been assigned to the Defense Intelligence Agency as an operations support specialist.
The three other transfers will be conducted privately, with the president observing. Trump also spent time with the victims' families. Trump told reporters as he left the White House for the trip that meeting the relatives of the country's fallen heroes "might be the toughest thing" he has to do as president.
President Donald Trump is heading to Dover Air Force Base to pay tribute to the four Americans killed in a suicide bomb attack in Syria this week.
He tweets: "Will be leaving for Dover to be with the families of 4 very special people who lost their lives in service to our Country!"
The Delaware trip hadn't been on the president's public schedule for Saturday, but he tweeted the news before he left the White House.
The bombing in Manbij was the deadliest assault on U.S. troops in Syria since American forces moved into the war-torn country in 2015.
The attack came about a month after Trump said the Islamic State group had been defeated and he was withdrawing U.S. forces from the country.
IS claimed responsibility for the attack.