The West's prime new tactical fighter, the fifth generation F-35 aka Lightning II, will come in three variants:
First there's the CTOL (Conventional Take-Off and Landing) variant, the F-35A, meant to replace ageing third generation fighters in the USAF and other air forces. It is the smallest of the three variants, yet it is the only one equipped with an internal cannon, the GAU-22/A. This is a 25 mm cannon, a development of the GAU-12 which is mounted on the USMC's AV-8B Harrier II, and which is primarily meant to engage ground targets.
Somewhat surprisingly for such an expensive aircraft, the F-35A is only expected to "match" the F-16 in maneuverability and instantaneous and sustained high-g performance. It should however vastly outperform it in stealth, payload, range on internal fuel, avionics, operational effectiveness, supportability, and survivability. It will have built in the functionality of the sniper pod, a device which today is mounted under the fuselage of, typically, third generation fighters like the F-16. The F-35 A variant is mainly intended to replace the USAF's "Fighting Falcon", beginning in 2013. Plans are that it should replace the A-10 Thunderbolt II starting in 2028, which not only seems impossibly far-fetched to me but also strange, since I cannot fathom how the slender airframe of the Lightning II could ever be capable of either operating from rugged airfields, or sustain the same battle damage an A-10 can take (and still be able to fly).
The F-35B is the short takeoff and vertical landing (STOVL) variant. It's similar in size to the A, and as such, equipped with a VTOL system as quaint as it is original, has less internal volume for fuel storage, armament, or avionics to detect and engage the enemy. Lift power is provided by a huge fan directly behind the cockpit, and a jet thrust that can be rotated downwards at the back:
This is how it works:
Plans are that the United States Marine Corps will purchase 340 F-35Bs to replace all current F/A-18 Hornet models (the A, B, C and D-variants), as well as its AV-8B Harrier II's.
Finally there's the F-35C, the Carrier variant. It has larger wings with foldable wingtip sections, stronger landing gear for not getting crippled on pitching flight decks, and larger wing and tail control surfaces for enhanced low-speed control. Of course a tailhook will be provided. With twice the range on internal fuel as an F/A-18C Hornet, the F-35C will be a worthy successor to the F/A-18E/F Super Hornet.
The United States Navy intends to buy 480 F-35Cs to replace its F/A-18A, B, C, and D Hornets, and backup the Super Hornets.