This image comes courtesy of Airliners.net. In deference to them and their hotlinking/copyright policy, I have refrained from posting the image here on OppoLock and instead will simply link it here. That said, it really is worth a look as it's an amazing photo.
The A-10A Thunderbolt II was developed to counter the massive numerical advantage of Soviet armor during the Cold War, particularly in the so-called "Fulda Gap" area of Germany where most NATO military planners assumed huge armor battles would just about automatically occur. Unusual of small tactical warplanes of its era, it forgoes swept wings and buried engines in favor of an appearance that almost looks pulled from a WWII-bound time machine (an appearance that lends to its nickname, the "Warthog" - incidentally, the name "Thunderbolt II" also honors the WWII P-47, a very excellent high-altitude fighter but also one of the world's first airborne tank killers). The straight "Hersey Bar" wing not only means great low-altitude handling (as pilots who fly Piper Cherokees can tell you) but is also an efficient planform for carrying tons and tons of expendable armaments (i.e. tank-killing missiles). Likewise, the engine arrangement is optimally efficient for its subsonic, high-bypass turbofan engines but also allows the wing to essentially shield them from both infrared detection and direct fire. The most imposing feature, however, is the GAU-8 Avenger 30mm cannon. Packing more kinetic energy than many weapon systems with a larger bore diameter, the Avenger is, contrary to popular belief, not actually intended to penetrate a tank's armor directly but rather to attack a tank's top armor, which traditionally is where the tank's thinnest armor is located. The reason why this tends to be is because few weapons systems are actually capable of a direct top attack against tanks.
The A-10 Thunderbolt II is one of those few weapons systems.
The A-10C adds the typical goodies found on contemporary fighters: computer systems that allow for improved targeting, LINK-16 compatibility (i.e., it can "talk" with Allied assets including satellites) and other "techie" upgrades. What's arguably most significant, however, is a change that isn't beneath the skin as so much as it is the skin: an extensive re-manufacturing process that adds life back into the airframe. Despite the host of survivability and durability improvements, the A-10C is potentially threatened by funding cuts in the face of Pentagon budgetary sequestration.