The IG-227 Hailfire-class droid tank, often simply called the Hailfire droid, is a Pentastar Alignment light vehicle available in all five eras. It is armed with two rapid fire anti-infantry blaster cannons and a long-range missile launcher.
Before the Clone Wars, the Hailfire droid was used by the InterGalactic Banking Clan to punish clients who failed to pay their debts on time. When approached by Count Dooku to join the Confederacy of Independent Systems, the Banking Clan pledged its support and donated the Hailfire to them (albeit in a non-exclusive deal).
During the first parts of the Clone Wars, the Hailfire droid was used extensively, most notably in the Battle of Geonosis, where they induced heavy casualties until destroyed by the airborne LAAT/i units. The droids limited warhead capacity led to its being pulled from the war until an aerial refresh droid could be designed. When put back into service, it once again became the scourge of slow moving vehicles.
After the execution of the Separatist Council on the orders of Darth Sidious, all Separatist-controlled droids, including any Hailfire droids, were deactivated. However, the Empire could not act against the Banking Clan, as doing so would send the galaxy into a recession; the non-exclusive deal meant that they could continue producing Hailfire droids, keeping a small number active to serve as a self-defense force.
After the Battle of Endor, the Banking Clan remained officially allied with the Empire, however it became the creditor of several major powers, including the New Republic. The capital of the Banking Clan, Muunilinst, was located in the heart of Grand Moff Ardus Kaine's new Pentastar Alignment, and the Moff used this leverage to convince them to donate several of the droids to the Alignment. Upon seeing the amazing combat potential the Hailfire had, Kaine contracted the Banking Clan to begin producing them on a larger scale once more. They would serve as the Alignment's primary siege unit until its dissolution into the Imperial Remnant.
The Hailfire droid is the artillery of the PA, and is arguably the best artillery in the game. At 1200 credits, the price is quite steep, but they are buildable from Light Vehicle Factories as opposed to Heavy Vehicle Factories for the other factions' artilleries. It is tougher than any other artillery unit in the game as well. Its primary value, though, is that it does not need to deploy to fire. Thus, it can fire while moving. Lastly, it has the best close-range anti-infantry defenses, with the equivalent of 2 anti-infantry turrets mounted on its frame.
All this does come at a cost, though. The primary disadvantage is that it has the shortest range of the artillery units (although still greater than a Turbolaser). The other disadvantage is that since it does not need to deploy to fire, it has the habit of chasing units that retreat out of range. This is dangerous, as it can lure the Hailfire right into a trap.