For Durbin, the Senate's second-highest ranking Democrat, it is his first trip to the U.S. base since he made controversial remarks last summer about U.S. reports of bad treatment by U.S. soldiers of militant combatants captured in Afghanistan and Iraq.
Critics at the time, including Democratic Chicago Mayor Richard Daley, said Durbin's statement improperly compared the interrogation at the prison camp to the methods of Nazis and other repressive regimes. Durbin said he was citing a report.
A teary-eyed Durbin later apologized for his remarks, saying he never intended disrespect for U.S. soldiers around the world.
Durbin spokesman Joe Shoemaker says Durbin and Allen left early Monday for Guantanamo and are expected to be there until late in the day.