In the years after World War II, the biggest fights were not between the United States and the Soviet Union. They were between the various armed services of the United States military — and things were getting ugly.
The Air Force and Army went through a messy divorce after World War II — mostly due to festering issues that cropped before the war. These issues were largely due to a controversial figure in Colonel Billy Mitchell. Mitchell, a long-time airpower advocate, had rubbed many people the wrong way, even though his experiments did highlight the fact that battleships were vulnerable to planes. His heavy-handed advocacy for airpower angered many in the Army while those who agreed with him felt the Army was shortsighted. He wouldn't live to see WWII, but the debate he started would live on.
So, in 1948, the top officers of the Army, Air Force, and Navy took a trip to Key West, Florida — but this was no spring break. The three services were there to hash out and define the responsibilities of each branch. The result was a "treaty" of sorts that became known as the Key West Agreement.
The is how the agreement broke things down: The Air Force would handle combat in the air and air transport but also promised to provide close-air support for the Army. The Navy and Marine Corps were to handle naval combat – including amphibious assault. The Army was tasked with fighting on land. What was interesting was that the Army was also allowed "such aviation and water transport" that was organic to providing support to combat units.
Now, the Key West Agreement was not a complete success. The Air Force tried to assert its nuclear bombers could do everything – and convinced the then-Secretary of Defense to cancel a supercarrier under construction. That triggered the Revolt of the Admirals, which didn't quite stop major cuts in naval forces.
The Korean War, though, forced the services to get their act together. Ultimately, the Key West Agreement has largely worked for over 70 years.