The U.S. F-16 is one of the most modified jet fighters in service. While most are still called the F-16C, there are actually six major mods, identified by block number (32, 40, 42, 50, 52, 60), plus the Israeli F-16I, which is a major modification of the Block 52. Another special version (the Block 60), for the UAE (United Arab Emirates) is called the F-16E. The F-16D is a two seat trainer version of F-16Cs. The various block mods included a large variety of new components (five engines, four sets of avionics, five generations of electronic warfare gear, five radars and many other mechanical, software, cockpit and electrical mods.)
The F-16 is the most numerous post-Cold War jet fighter, with over 4,200 built, and more in production. During The Cold War, Russia built over 10,000 MiG-21s, and the U.S over 5,000 F-4s, but since then warplane has plummeted about 90 percent. But since the end of the Cold War, the F-16 has been popular enough to keep the production lines going.
The F-16 can also function as a bomber and ground attack aircraft, although not as effectively as the air force folks would have you believe. It can carry four tons of bombs. In air-to-air combat, it has shot down 69 aircraft so far, without losing anything to enemy warplanes. It was originally designed as a cheaper alternative to the heavier F-15.
The two most advanced versions of the F-16 are in use by foreign air forces. The UAE has 80 "Desert Falcons" (the F-16E) which is optimized for air combat. It is a 22 ton aircraft based on the Block 52 model, but with an AESA (phased array) radar and lots of other additional goodies.
The Israeli F-16I is optimized for bombing. It's a 24 ton, two seat aircraft, and is probably the most capable F-16 model in service. It's basically a modified version of the Block 52, equipped with a more advanced radar (the APG-68X) and the ability to carry Israeli weapons like the Python 4 air-to-air missile and the Popeye 2 air-to-surface missile. Costing $45 million each, the F-16I has an excellent navigation system, which allows it to fly on the deck (a few hundred feet from the ground), without working the pilot to death. The aircraft can do this at night or in any weather. The F-16I can carry enough fuel to hit targets 1,600 kilometers away (meaning Iran is within range). The aircraft uses the latest short and long range air-to-air missiles, as well as smart bombs. Electronic countermeasures are carried, as is a powerful computer system, which records the details of each sortie in great detail. This is a big help for training. The F-16I is basically optimized to deliver smart bombs anywhere, despite dense air defenses. This further increases Israel's military power versus its neighbors. Israel has received 102 new F-16I fighter-bombers in the last five years. Added to this will be another 125, as older F-16s are upgraded.