The difference of the branches is the official mission/purpose each has. And the way manpower is distributed.
The Marine Corps also has fighter pilots.
The official mission of the Marine Corps is established in the National Security Act of 1947, amended in 1952. Marines are trained, organized, and equipped for offensive amphibious employment and as a “force in readiness.” According to the Act, Marines stand prepared to meet mission requirements.
The seven elements of the Marine Corps mission:
a. Provide Fleet Marine Forces with combined arms and supporting air components for service with the United Stated Fleet in the seizure of defense of advanced naval bases and for the conduct of such land operations as may be essential to the execution of naval campaign.
b. Provide detachments and organizations for service on armed vessels of the Navy and security detachments for the protection of naval property at naval stations and bases.
c. Develop, in coordination with the Army, Navy, and Air Force, the doctrine tactics, techniques, and equipment employed by landing forces in amphibious operations.
d. Provide Marine forces for airborne operations, in coordination with the Army, Navy, and Air Force, according to the doctrine established by the Joint Chiefs of Staff.
e. Develop, in coordination Army, Navy, and Air Force, the doctrine procedures, and equipment for airborne operations.
f. Expand peacetime components to meet wartime needs according the joint mobilization plans.
g. Perform such other duties as the President my direct.