The A-10 is built for high-survivability, featuring titanium construction and multiply-redundant systems, but its most distinguishable quality is the nose-mounted GAU-8/A Avenger Gatling gun, firing depleted uranium shells capable of shredding a tank in as little as a six-shot burst. It was used occasionally as precision attack weapon during the First Tiberium War, but GDI more often than not armed it with napalm bombs that can blanket area targets such as troop concentrations or fortification clusters with an intense firestorm, giving Nod an ironic taste of their highly-inflammable medicine. After the First Tiberium War, its battlefield presence would be displaced by that of the Orca bomber, a VTOL aircraft that can be deployed from bases much closer to the frontline and respond to any situation in a much shorter notice.
The A-10 airstrike consists of one to three A-10s flying in and attacking a designated area with napalm bombs. The airstrike is mostly effective against infantry, as well as lightly armoured buildings and vehicles.
In the GDI campaign missions, the A-10 airstrike becomes available if the player destroys all Nod starting SAM sites on the map. What this means is that if you destroy a SAM site and it is later rebuilt by the AI, the new SAM site will not count against you gaining the airstrike capability, only the ones which were present when the mission started. As a result, in the later GDI missions when the AI is more likely to rebuild SAM sites, you need only to destroy each SAM once in order to obtain the airstrike ability. A-10s can then be deployed against targets despite the presence of SAMs, and no penalty is incurred even if any are shot down.
In the Nod campaign missions, A-10s will periodically attack you. More often than not, the A-10s will attack whatever unit or structure you have closest to the upper-left corner of the map, so simply leaving a sacrificial minigunner (or a tank, which can be repaired) in that position can prevent damage to the rest of your forces. Also note that the computer-controlled A-10 will actually acquire a target and attempt to chase it down, unlike the airstrike in the GDI campaign which can only be directed against a target area. Destroying the GDI communications center in a given mission will prevent airstrikes from being directed against you.