When World War II started, he was called up as a colonel and assigned to the United States Military Academy. The head of the physics department there, Gerald Counts, was reassigned to Europe, and Bartlett stepped in as acting head of the department.
Upon the outbreak of World War II, he was mobilized as a colonel and posted to the United States Military Academy. Following the reassignment of Gerald Counts, the head of the physics department, to Europe, Bartlett assumed the role of interim head of the department.