Answer :

If you are a member of the United State Navy, then you belong to the department of defense. U.S Navy or military works for the United States’ peace and security. Thus, U.S Military is in charge of their country’s defense. Department of Defense is headed by the secretary of defense. Under the department of Defense are the 3 subordinates:
=> The department of the Army
=> The Department of the United States Navy
=> The Department of the Air force