Why does each service branch have repeated functions? Inf., Avn., Boats, Med, HR/Pay, etc? Save $ with one branch with specialized functions?

Sorry, Major, but no Air Force fixed-wing pilot is ever going to land on a carrier.

Tradition is not reason enough to waste our military capabilities. With a smaller military and budget concerns, it is important to maximize where troops are placed.
Why does each service need its own aviation, medical service, payroll system, personnel system, logistics, transportation, etc.? Why have infantry, armor and artillery in the Marines and the Army? Why have boats in the Army, Marines and Navy? I am sure there are many more examples.

Here is my proposal:

Consolidate all the branches into one military (Department of Defense) service with one medical, human resource, pay, supply and other support systems. All support positions (hospitals, supplies, finance, personnel) will follow one system. This will reduce the number of troops needed to fill those support positions by probably about one-quarter to one-third of the current level. These positions can be moved to the combat arms.
A lot of the permanent garrison positions could be civilians, thus freeing up more troop numbers for the combat arms.

There would be one branch of infantry, armor, artillery, aviation, naval assets instead of being spread across all services. Internally, there can be specialized units for unique missions.

Instead of each service having its own special operators, have one the can also have specialized functions internally.

Consolidate bases into about seven joint locations; one forward-operating base each in the Pacific and Europe; one each, west coast, east coast, southern US / Texas (all with lots of training / maneuver space, private airstrips and docks for ships); central US and somewhere in the northern Midwest (all with lots of training / maneuver space, and private airstrips).

Being consolidated assets, there would be less time needed for emergency coordination as procedures would be internal to that location and under one commander.
This would also reduce the number of senior officers (specifically, flag officers), the need for a Joint Chiefs of Staff and the number of people needed at the Pentagon.

Another cost savings would be in the minimized number of types of uniforms, awards, accoutrements, and Service Schools / ROTC programs.

I am sure I am overlooking many other areas. I am also sure that there are tons of costs involved with such a transition.

I look forward to the responses I get.

It's very practical. Each service has its own operating environment which requires a unique philosophy, doctrine, culture, policies and procedures. Each service has optimized its procedures to maximize effectiveness in their own environment.

Consider HR/Pay types. Would they all be trained in the procedures used both aboard ship and also in the desert? Would they have to learn 4 sets of regulations?

Different procedures make for a different mindset: Air Force pilots use mile-long runways and gradually settle down on the glide path until touchdown halfway down the runway. Navy pilots won't put a foot of runway behind them; they'll put it down on the numbers. Different policies: In the Navy, if there is a fire, all hands attack the fire until Damage Control arrives. In the Air Force, all hands evacuate and wait for the Fire Dept. Different capabilities: A common specialty is dermatology. In the Army, derm doctors are needed right up front, as combat wounds almost always involve the skin. But how many doctors can you fit on a ship? In combat: The services don't have the same radios or the same language.

Importantly, each Division commander or Wing commander has under his personal command all the resources required to prosecute war without needing some other commander to provide supply, transportation, housing, etc. Very effective and efficient in war. Don't change it.