Vice Chairman of the Joint Chiefs of Staff
The U.S. Vice Chairman of the Joint Chiefs of Staff is the second most senior officer of the U.S. military. His tasks are not fixed, but those that are assigned by the Chairman of the Joint Chiefs of Staff, although he does replace Chairman of the Joint Chiefs of Staff in his absence or disability. The position was created in 1986.
Though the Vice Chairman was not originally included as a member of the JCS, Section 911 of the National Defense Authorization Act of 1992 made him a full voting member of the JCS. There is also a three-star Assistant to the Chairman. Note that none of the Chiefs are in the operational line of command, which runs from the National Command Authority to the Unified Combatant Commanders.