The Joint Strike Fighter is being delivered to three branches of the US military in three different versions. The Air Force will be the biggest customer by far, ordering 1,736 A-variants. The F-35A is a traditional takeoff / landing model, needing about the same length runway as an F-16. It will replace the F-16 starting in 2013 and matches the F-16 in flight performance but is superior to the Falcon in range and payload capacity, even though it is the smallest JSF variant. The A-model will also replace the A-10C’s close air support role in 2028, but further modifications are expected to be made to the F-35 to make it more effective at flying “low and slow.”
The F-35B will be delivered to the USMC by 2012 to replace the AV-8B Harrier. Like the Harrier, the F-35 will be able to land vertically and takeoff in very short distances. The B could also replace the rest of the Marines’ aging fleet, like the F-18, and even take on electronic warfare roles. As many as 609 could be delivered, but cutbacks are expected.
The F-35C carrier variant will begin deliveries in 2015. This will be the Navy’s model, designed to takeoff using a ship catapult and land with a cable / tale hook system. It will be the largest variant and will replace the F/A-18 A-D Hornet. It will fly along side the Super Hornet and Growler electronic warfare plane. 480 are on order. (See more about the F-35C in the F-35C Characteristics post).
The only gun on baord the Joint Strike Fighter will be a 4-barreled Gatling cannon. The 25mm GAU-22 will carry about 200 rounds and will fire at a rate of 3300 rounds per minute. This means that although the gun will have extremely rapid and powerful firing capabilities, the entire stock of ammunition will be used up in less than four seconds. This will be less of a problem for the F-35 than it would be for fourth generation aircraft because the F-35 relies on its missiles so heavily for offense and will avoid dogfights as much as possible. The gun would only be used for defense in the projected rare case that a dogfight does occur. When missile technology first came about, experts believed that dogfights would become extinct. The first new planes in the missile era, like the F-4 Phantom, carried no gun and were outmatched when the inevitable close range battle broke out. The aviation community has since learned its lesson as all modern American fighters carry a gun or cannon. The F-35A conventional fighter will carry its gun internally mounted over the pilot’s left shoulder, similar to the mounting on the F-22. The B and C will carry the gun in an attached pod under the aircraft that will allow for slightly more rounds or the option to detach the gun and carry extra fuel, missiles, or whatever the mission calls for. The GAU-22 is designed and manufactured by General Dynamics and is based on the companies successful GAU-12 used on the Harrier. The main difference between the two is that the newer gun has only four barrels to the GAU-12’s five. This will make the gun significantly lighter and more compact. This change will also reportedly make the gun more accurate while maintaining a similar muzzle velocity. 
