 Lahm went instead to Chaumont as the section's liaison to GHQ AEF until February 23, 1918, when he was moved to Colombey-les-Belles in the same capacity to the Air Service, Advance Section, Services of Supply, where he supervised the tactical training of balloon companies before their assignment to the front as artillery spotters.On June 3, 1918, an air service for the soon-to-be-activated U.S. First Army was set up at Toul, with Foulois in command.Lahm was chosen to be his chief of staff, and remained so until after the Battle of Chateau-Thierry, when Foulois voluntarily turned over his command to Brig.