Simplify the following text for a Grade 8 native English-speaking person.
Original: It was created in order to give civilian leadership and administration to the United States Navy and the United States Marine Corps . The Secretary of the Navy is in charge of the Department of the Navy , and the Department of the Navy is under the authority of the Department of Defense .
Simplified: The Department of the Navy consists of all elements of the United States Navy and the United States Marine Corps .