The United States Defence Force (USDF) is run by a former Fleet Admiral going by the name of Sycron. And was one of the first militaries to contain all 4 branches within the United States Military, which are the US Army, US Navy, US Air Force, and the US Marines. The branches are run by:
CSAF (Chief of Staff of the Air Force, General - WalkingBootz)
CSA (Chief of Staff of the Army, Lieutenant General - davidhif2)
CNO (Chief of Naval Operations, Admiral - MEXYYY)
CMC (Commander of the Marine Corps, Major General - Acyr)
All of those members listed above are members of the JCS (Joint Chief of Staff) and the CJCS (Chairman to the Joint Chief of Staff) is Fleet Admiral, Controllable.
Then there is the NSC (National Security Council) who is run by the Secretary of Defense Mr. Sycron