The way I read it, 'unification' was a big deal after WWII in creating a more streamlined armed forces. Did some of the plans call for Marines to be folded into other services? If so, why was this a thing given how much love there must have been for the military after the war and with Communism spreading?
The post war draw down and reorganization that eventually led tot he formation of the modern Department of Defense saw huge battles over turf rage in Washington.
It seemed that everything was on the table, and especially with a newly ascendant independent Air Force pushing their own vision for what future warfare would look like. There were questions over everything from why we needed a Marine Corps when the Army had proven time and again fully capable of taking and holding enemy positions from the sea. To why the Navy needed all these damn expensive aircraft carriers and planes when long range bombers flown by the Air Force could just drop nukes on the enemy and not need all those islands seized as forward airfields as the range of aircraft increased.
The other factor I would say you are missing from it is that in addition to the structural questions raised by the National Security Act of 1947 creating a single boss for all the services at the cabinet level was big. Previously the Secretary of War and the Secretary of the Navy we peers and both Cabinet members so that the Marines and Air Corps if the junior partner on their teams, always had a Secretary in "their" corner who could plead to the President. With all 3 service secretaries(since the Marines still didn't get their own) now having to answer one Secretary of Defense each service now had to do more to make their case in other ways, often at the expense of the others. And taking away a redundant to some branch, or all the Navy's planes, was a good way to make sure the same size pie could go further in many circles.
Underlining all this though was the MASSIVE draw down in size and funding of the military in the late 40's. Until Korea demonstrated that the Cold War would not allow for anything but a large standing force the US tried to do what it had done time and again, send most everyone home once the war was over and save money. For reference take a look at the charts halfway down from this piece from the Council on Foreign Relations: https://www.cfr.org/report/trends-us-military-spending
Or here: http://www.usgovernmentspending.com/defense_spending
Notice especially the HUGE dip following 1945, reversed only by the need of Korea, where it stays at about 10% GDP through to the Nixon years. But to give this some real numbers the US Navy for instance went from nearly 7,000 vessels under commission of all types in 1945, to about 850 in 1947, to less than 650 in 1950 just before the start of US involvement in Korea!
The rapidly shrinking pie created some very bitter battles between the services and it is actually rather remarkable that all 4 came out with their core missions and nature relatively intact.
Fascinating and interesting , thank you. Makes sense in hindsight given lack of interest in military spending after Americans had war fatigue.
I've also heard that Truman - an Army vet - had no love for the Marines.
It's also not surprising that 1949 produced 4 Hollywood movies about each of the armed forces. Sands of Iwo Jima, 12 O'clock High, Battleground and Task Force. They knew Hollywood could help them. Ultimately - the Marines were the big winner in that fight.