Airman Jack Teixeira has been charged in Boston court.
He faces up to 15 years in prison.
Charges relate to leaked documents.
Leaked documents revealed US assessments of the war in Ukraine.
They also contained sensitive information about American allies.
The leaks were posted in a Discord chat room.
Teixeira held a top secret security clearance.
He used his government computer to search for the word "leak".
US President Joe Biden thanked law enforcement.
He directed military and intelligence to secure sensitive information.