Question: does the army fall under the department of defense

Answer: Yes, This is a list of Agencies under the United States Department of Defense (DoD) which was formerly and shortly known as the National Military Establishment. Its main responsibilities are to control the Armed Forces of the United States. The Department was established in 1947 and is currently divided into three major Departments--the Department of the Army, Navy and Air Force--and has a military staff of 1,418,542 (553,044 US Army; 329,304 US Navy; 202,786 US Marine Corps; 333,408 US Air Force). The DoD is headed by the Secretary of Defense. The current defense secretary is James Mattis.