Incendiary ammunition was developed during World War I by the British Empire. Initial designs used phosphorus as a tracer filling, ignited when fired from its weapon. Its use was heavily regulated to avoid breaking the St. Petersburg Declaration of 1868.
Incendiary ammunition was created to counter the threat of German airship bombing runs against the homeland. The airships operated well above the flight ceiling of contemporary aircraft, and received insignificant damage from any conventional ammunition able to reach it from the ground. Incendiary ammo fired from fighter aircraft was able to ignite the hydrogen balloons carried within the airship's fuselage.
During World War II, incendiary ammo would continue to find use in aircraft, as it could also ignite an enemy's fuel tanks. These later designs were capable of igniting on impact, instead of immediately after firing, greatly increasing their effective range. Modern incendiary ammo is able to delay ignition to ensure damage after penetrating armor, and can be mixed with explosive fillers to create explosive or fragmenting ammunition.
Incendiary Ammo is a vehicle gadget available to Fighter Planes using the Dogfighter Package. It replaces the standard ammunition with 30 rounds (15 rounds × 2 HMGs) of incendiary ammunition, inflicting greater damage against aircraft. It is able to quickly inflict mobility damage against wings.
Against other targets, incendiary ammo is not much different from standard rounds, inflicting considerable damage to infantry and light vehicles, but no damage to heavy vehicles.