What includes the leaders of the US Army Navy Air Force and Marines?

Answer 1

That "organization" is called the US Joint Chiefs of Staff. It is composed of 6 members, all of which are a 4-star rank: the highest ranking military member of each branch, called the Chief of Staff of the Army, Chief of Staff of the Air Force, the Chief of Naval Operations and Marine Corps Commandant. In addition, the President selects a Chairman and a Vice Chairman from amongst the services (that is, the Chairman and Vice Chairman are not one of these 4 people, and may be from any branch).

In reality, it is currently nothing more than a paper organization. The person selected by the President to be the Chairman of the Joint Chiefs is generally seen as the primary military adviser to the President, and usually works in close contact with the President. The Chairman and the National Security Adviser are the two most influential persons around US Military operational policy - the Sec of Defense and the remaining Joint Chiefs are more administrative positions, dealing with the running and organization of the military (or their specific branch) and not operational planning or policy.

With the modern restructuring of the US armed services to focus more on "operational" groupings, rather than service-related groupings, the President spends a much larger amount of time (usually mediated or assisted by the Chairman) talking to operational commanders - the 2- or 3-star leaders of various specific commands, who have direct control over the operations in their theater.

In short, while the Chairman of the Joint Chiefs is a very powerful position, the actual Joint Chiefs organization is really not one involved with deciding policy or strategy - rather, it is a place where the administrative heads of the various branches coordinate policy implementation inside the military itself.

Answer 2

The President of the United States is Commander-In-Chief of the United States military as a whole, which, on top of the branches listed in your question, also includes the Air Force and Coast Guard.

Answer 3

The Joint Chiefs of Staff.

Answer 4

joint chiefs of staff