Kdtyjb

Why are aircraft such as the legacy F-14 and now the F/A-18 used by the US Navy carriers?

It seems to me that developing a new aircraft from the ground up is very expensive. Is it not possible to have converted F-16 or F-15's for carrier operations? Obvious modifications such as folding wings, stronger undercarriage, hook, etc. I'm sure there are many more I'm not aware of.

Is the reason that these aircraft (F-16, F-15) are not suitable for carrier operations, even with modifications?

Isn't this what the Russian Navy did with their fighters? The carrier versions of the MiG-29 and Su-27?

What are the reasons the US employs unique carrier aircraft? Is the reason political? Technical?

It's technical, not political

The F-35 was an attempt to do exactly what you propose, lowering costs by planned sharing of 80% of parts across variants, but it turns out that the USN's F-35C costs over twice as much as the USAF's F-35A, and only shares 20-25% of it's parts. The project has been a disaster practically since day one, and the services are already working on separate replacements tailored from the start for their very different missions.

Per Wikipedia, the USN decided a carrier variant of the F-15 would be too expensive and the YF-16 was inherently not suitable for carriers, so they modified the YF-17 into the F/A-18 by making the changes you propose. The USAF didn't need those changes, so they stuck with the faster and cheaper YF-16, which became the F-16.

Keep in mind that each US aircraft carrier holds the fourth largest air force in the world, and there are ten of them. That sort of volume means the USN can afford to customize planes for their exact needs, whereas other countries with far smaller carrier fleets may be forced to make do with planes that the USN considers "unsuitable" or "too expensive", especially if they aren't US allies.

The YF-17 is the answer to your question. It is the predecessor to the F/A-18, and was designed as a land-based fighter. The YF-17 is much lighter than the F/A-18, because it does not need to carry equipment for carrier landings. Adding this equipment makes the aircraft heavier, compromising performance. You then need to compensate for the added weight, but the airframe may not have space for different engines or additional fuel.

Overall there are just so many changes to be made, that as StephenS points out with the F-35, you don't end up saving money by having a few things in common.

There is a saying: "Jack of all trades, master of none." That is, if you design something to be useful in all situations, it will not excel at any of them.

The F-4 Phantom did do the reverse, starting as a Naval aircraft before later also being adopted by the USAF and USMC.

The needs to operate on a carrier are different than the needs for a land based aircraft. They are subtle, but significant. As others have pointed out, the F-35 attempted to address these issues and wound up way over budget. (It was made even more complicated by the addition of a STOVL version for the Marines, the F-35B).

CATOBAR aircraft differ from conventional aircraft in subtle, but very important ways. Takeoff and landing on a carrier is significantly different. Its landing gear must be significantly strengthened to handle the "controlled crash" of landing on a carrier deck, and the sharp deceleration of the arresting cable, and the sharp acceleration of the catapult when taking off. It needs a strong arresting hook to snag the cables on landing. The engines can't melt the carrier deck or blast shields on takeoff.

The short flight deck and tricky approach requires a lower landing speed, and better low speed handling requiring a significantly larger wing area. This also gives more lift to keep the same cruising range despite all that extra weight.

The limited space on a carrier often requires folding wings, the joints must be able to handle all the stresses of combat maneuvering. More weight and more complexity.

The aircraft must be able to be maintained and repaired while at sea with the stores and equipment available to a carrier. It must be resistant to salt water, particularly hard if you're using advanced skins to reduce radar cross-section. The limited storage space means it ideally has to share the same fuel and weapons and other consumables with other carrier aircraft.

Finally there are self-inflicted inter-service incompatibilities. The US Navy and Air Force use different aerial refueling systems requiring different parts and plumbing.

Most navies look at all these extra requirements (and weight, always weight) and are satisfied with lower performance, usually lower takeoff and landing weights meaning less fuel and less stores. For example, ski-jumps like on the Admiral Kuznetsov are simpler and cheaper than catapults and reduce the strain on the aircraft making conversion to naval simpler, but they limit the takeoff speed and weight of the aircraft. Better to have some sort of fixed-wing air capability within their budget than none.

The US Navy doesn't have any of that. They want a naval aircraft that is the equal or better than land based aircraft. That comes at a cost in weight, money, and complexity.

Another reason that carrier aircraft tend to be quite different from land based aircraft is the environment in which they operate: lots of salt. Consequently, carrier aircraft contain a much greater degree of corrosion resistant components, raising the price and in some cases the weight.

Several naval aircraft have been adopted by land air forces. The USAF and several other air forces adopted the F4 Phantom. USAF also used the A1 Skyraider. Several land based air forces have used the US A4 Skyhawk and F18 Hornet in a land based role. The Hawker Sea Fury was used by Iraq in the 1950's and 1960's. The Philippines operated F8 Crusaders as land based aircraft in the 1980's.

Land based aircraft designs have been adopted for carrier use, albeit with major changes. The Supermarine Seafire was a conversion of the Spifire. In the US, the F86 Sabre was produced in a naval variant, the FJ2/3/4 Fury. The Russian MIG29 has been produced in a naval variant for operation on their carrier. The previously mentioned Hawker Sea Fury was an adaptation of the Hawker Tempest land based fighter.

Plus a couple of desperation measures: The Hawker Hurricane was used at sea on the CAM merchant ships to defend against FW200 Kondor aircraft, but that was a one time use only with no ability to land at sea, and the pilot was often lost in the frigid North Atlantic waters. Plus the one time use of B25 bombers from the USS Hornet.