The Deparment of the Navy is not the same thing as the United States Navy. Did you read the text of the link?
Suppose it were the Department of the Marine Corps (which, notably, it is not), and it contained the US Marine Corps and the US Navy. It would be qualitatively different.
In what way? Look, there’s New York the State and New York the city. The fact that they share names is irrelevant to their organizational structure. Albany isn’t a subset of New York City. Same thing with the Department of the Navy and the U.S. Navy.
The Chief of the Naval Operations, Admiral Vern Clark, USN, is a member of the United States Navy, hence the rank in front of the name and the USN behind. He runs the U.S. Navy. The Secretary of the Navy, The Honorable Gordon R. England, is not a member of the United States Navy, or for that matter, of the United States Marine Corps. He’s a civilian. He runs the Department of the Navy, which also includes the U.S. Marine Corps. He’s a cabinet official, and is also the Acting Deputy Secretary of Defense.
I find it interesting that the USMC does not have its own doctors or chaplains – they’re Navy officers – but does have its own lawyers.
Minor Correction (that has nothing to do with the argument :D) CNO is ADM Mike Mullen
I’m an ex-Marine.We are part of the Navy.As I remember my lore,Marines were snipers on ships.The assignments became more specialized into a corps.The marines are small units sent to kick ass until the larger army can get there.The Navy provides transportation
I’m an ex-Sailor and I remember it the way you do 
To the ex-Marine and ex-Sailor: Please peruse the links mentioned above. The Department of the Navy is clearly composed of two Uniformed Services: the Navy and the Marines. Thus the Marines is not part of the Navy; it’s one of the two Uniformed Services in the Department of the Navy.
Yes, and thus the Navy and Marines are part of the Navy. Peruse them yourself.
Already did. Apparently, though, I can parse the English language a tad better than you are doing. There is a difference between the Navy and the Marines. The Marines aren’t part of the Navy. The Marines, according to the United States government, not according to your wishes, are part of one governmental department which just so happens to be composed of two different groups: the Navy and the Marines. Different groups, not part of each other, but both part of a particular governmental department, which, btw, is not named the Navy, but rather Department of the Navy.
The Navy and Marine Corps are perhaps best described as symbiotic services.
Both are hosted as creatures of the Department of the Navy. They have separate representation on the JCS.
The Commandant of the Marine Corps does not report to any uniformed Naval Officer.
However, there has never been an O-11(five star) rank in the Marine Corps: no “Generals of the Marine Corps”.
The Marines grew in their mission, but never separated from the Navy. Contrast this with the separation of the Air Force nee Army Air Forces from the Army. The Air Force has its’ own Department, and there has been one O-11 Air Force: H.H. Arnold, who was an Army O-11 before the AAF separated.
So the Marine Corps is its’ own service, but it didn’t separate from the Navy as completely as the Air Force did from the Army.
The Navy and Marine Corps share some critical infrastructure, and their missions are heavily linked.
Marines were initially literally “ship’s soldiers”: they were basically infantry stationed on ships. As time went on, the MC grew in size, and took on larger ground missions, becoming a Navally-deployed, amphibious ground force.
Think about this very carefully.
Department of the Navy
Think about this very carefully:
The Department of the Navy is composed of two uniformed services; to wit, the Navy and the Marine Corps. Those two uniformed services are separate services which just so happen to fall under the same governmental department. Your insistance that the Marines are part of the Navy, as opposed to a part of the Department of the Navy, is akin to asserting that the Navy is part of the Army since they both are part of the Department of Defense.
No it’s not quite the same, but it is all semantics nonethless. The trouble is ‘navy’ alone is ambiguous. Is the marine corps a part of the navy?
Yes it’s part of the Department of the Navy
No it’s not part of the United States Navy
If you just say ‘navy’ alone you can argue all you want, but you’ll be arguing at cross purposes.
As a linguist, I can confidently say that semantics is not a bad word. The Navy is one particular uniformed service. The Department of the Navy is not one particular uniformed service. That’s not semantics. It’s organizational structure.
Charts and graphs are sometimes quite pretty, but to truly understand the relationships they convey takes real life experience. The fact of the matter is that the Marines are part of the Navy. As a linguist, I am sure you can understand the difference between understanding the tree structures of a language and speaking that language itself.
So in the old German Kreigsmarine or Italian Regina Marina, would they ask if the navy was part of the marine?
No, and neither would the officer of marines in Billy Budd.
Oh for crying out loud!
If you use the term “Navy” to an average American, I guarantee they will think you are referring to the U.S. Navy, not the Deparatment of the Navy.
When I tell people that I was in the Navy, they invariably understand that I was in the U.S. Navy.
There is not a U.S. Marine out there who would refer to him- or herself as being “in the Navy.”
For all intents and purposes, the term “Navy” (here in the U.S.) means the U.S. Navy.
That is why it is incorrect to simply state that “the Marines are part of the Navy.” You are implying that the U.S. Marine Corps is part of the U.S. Navy, which it is not.
It is correct to state that the Marines are part of the Department of the Navy.
I’m not disagreeing with you and i’m not crying out loud. Here you have a sailor and a marine patiently explaining to you that the Marines are Part of the Navy. In fact an integral part. Many of those posting in this thread are not aware of the close historical relationship the two services have, and probably many of them have no idea who the Merchant Marines are. Why, they are marines! But…they live on and operate ships. Oh the confusement. Don’t let the stereotypes confuse you all - there is a very fine, and sometimes indiscriminate line between what a sailor is, and what a marine is.