The Coast Guard, despite being the oldest armed service, has always been the bastard child of the military. It has always been my understanding the the Commandant of the Coast Guard met with the JCS in their advisory role to the President even though he was not under the command authority of SecDef. (It should be noted that there are Coast Guard units and personnel operating in the Iraq Theater of War and under the operational authority of the theater commander.)
This has to do with the esoterics of the "chain of command" at the highest levels. The President, as Commander in Chief, sits at the pinnacle of the chain of command, but the Vice President is NOT in the chain of command. The
administrative hierarchy is distinct from the chain of command. For the DoD armed services, The chain of command runs from the President to the Secretary of Defense, and from the Secretary of Defense to the commander of the combatant command. It's noteworthy that the Chief of Staff (a staff position, i.e. administrative) is not in the chain of command. Obviously, however, the chain of command for Coast Guard personnel does not typically run through the Secretary of Defense. Usually, it ran through the Secretary of Tranportation (Secretary of the Treasury when I was in) and now (apparently) through the Secretary of Homeland Security. That command chain, however, does not have a congruent staff function if there's no DHS function equivalent to the JCS (which is a DoD function). That's why the Commandant of the Coast Guard works in concert with the JCS, as I understand it. (Remember, the JCS operationally advises the President, the SecDef, and the NSC ... each directly even though reporting to SecDef for adminstrative/budget purposes.) So the chain of command for the U.S. Air Force (for instance) would be POTUS (the President of the United States), the Secretary of Defense (SECDEF), the Secretary of the Air Force (SECAF), the Under Secretary of the Air Force (USECAF), and the combat commander of either a unified or specific command. Note that under this arrangment, the Chiefs of staff are an advisory group to the U.S. President and do not lie in the chain of combat command of the military.
See
http://www.everything2.com/index.pl?node=United%20States%20Military%20Chain%20of%20CommandIn short, as I understand it, the "Joint Chiefs of Staff" in effect has a different compostion depending on whether we're looking at it from POTUS's perspective or SecDef's perspective. When POTUS is advised by the JCS, the Commandant of the Coast Guard is in attendance. For budgetary/administrative purposes, the JCS does not include the Commandant of the Coast Guard.
From Wikipedia ...
"
The Coast Guard Commandant is Chief of the Coast Guard IAW Title 18 USC 40. He is responsible for all coast guard matters and sits on the Joint Chiefs of Staff. He reports to the President, the Secretary of Homeland Security and the Secretary of Defense. "
http://en.wikipedia.org/wiki/Commandant_of_the_Coast_Guard Further...
"
The Coast Guard carefully coordinates its international efforts to ensure that its limited resources are best used to achieve U.S. foreign policy and national security objectives. It is within this framework that the Coast Guard operates overseas and engages internationally for the benefit of the United States and to execute Coast Guard missions. Plans are integrated with the other military services through the Joint Chiefs of Staff and regional Commanders-in-Chief (CINCs). Coast Guard efforts in support of the CINCs are integrated into their respective Theater Engagement Plans."
http://usinfo.state.gov/journals/itps/1299/ijpe/wartko.htm I see the defining authority for the
DoD's JCS is the Goldwater-Nichols Act of 1986 (10 USC 5) ...
151. Joint Chiefs of Staff: Composition; Functions
(a) Composition. There are in the Department of Defense the Joint Chiefs of Staff, headed by the Chairman of the Joint Chiefs of Staff. The Joint Chiefs of Staff consist of the following:
(1) The Chairman.
(2) The Vice Chairman.
(3) The Chief of Staff of the Army.
(4) The Chief of Naval Operations.
(5) The Chief of Staff of the Air Force.
(6) The Commandant of the Marine Corps.
One of the Coast Guard Service Badges is the "Joint Chiefs of Staff Badge" ...