In Hearts of Iron, you play as a country during WW2.
As Germany, you face threats from Britain (ships, fighters and bombers), France (mostly land forces) and Russia.
What do you build?
Air superiority fighters win dogfights (F22 today) but are only useful vs Britain.
Close Air Support (A10 today) beat tanks, but lose in the air.
Multirole fighters (F35 today) work in all three theaters, but not as well as the specialists.
Given that the next war might be vs Russia (Crimea situation), Taiwan / China (Naval), or maybe even terrorists in Africa or Middle East, multirole is the obvious airplane to build today.
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So Air Force wants a multirole fighter that can take off from airstrips / airports.
Marines want a multirole fighter that can take off of Wasp Amphibious Assault Ships (ramp launch)
Navy wants a multirole fighter that can take off of their Aircraft Carriers (catapult launch).
This gives F35A, F35B, and F35C variants. But since they all wanted a multirole fighter, it makes sense to try to make the three variants as similar as possible. You want to standardize the gun, standardize the bullets, standardize the fuel, standardize the software.
As Germany, you face threats from Britain (ships, fighters and bombers), France (mostly land forces) and Russia.
What do you build?
Air superiority fighters win dogfights (F22 today) but are only useful vs Britain.
Close Air Support (A10 today) beat tanks, but lose in the air.
Multirole fighters (F35 today) work in all three theaters, but not as well as the specialists.
Given that the next war might be vs Russia (Crimea situation), Taiwan / China (Naval), or maybe even terrorists in Africa or Middle East, multirole is the obvious airplane to build today.
-----
So Air Force wants a multirole fighter that can take off from airstrips / airports.
Marines want a multirole fighter that can take off of Wasp Amphibious Assault Ships (ramp launch)
Navy wants a multirole fighter that can take off of their Aircraft Carriers (catapult launch).
This gives F35A, F35B, and F35C variants. But since they all wanted a multirole fighter, it makes sense to try to make the three variants as similar as possible. You want to standardize the gun, standardize the bullets, standardize the fuel, standardize the software.