Admiral Mullen is the Chairman of the Joint Chiefs of Staff, not the Chief of Staff of the Army. He is an admiral in the US Navy. The Army has its own Chief of Staff. In the US, we have seperate military services: Army, Navy, Air Force, and Coast Guard. The Marines are part of the Navy.
Syrian rebels call for regional alliance against Russia and Iran (Reuters)
from the article: U.S. army chief: Iraq war has sapped ability to fight Iran