M990 electrothermal-chemical smoothbore cannon

The M990 electrothermal-chemical smoothbore cannon is the primary armament of the M820 Scorpion, introduced into widespread service in 2557.

Overview
Unlike the M512 cannon mounted on the M808, or even the M310 cannons mounted on the M850 Grizzly, the M990 fires a much larger 150mm shell, and is capable of firing guided munitions and projected future advances in energetic propellants. ONI-operated Scorpions use an experimental shell, and Hannibal Weapon Systems has produced a prototype that uses an XM820B4 DEW mounted within the barrel.

The M990 is extremely effective at penetrating heavy armor, including Type-58 Wraith tanks, and even Forerunner weapons such as the Z-510 focus turret. It is less effective against nimble aerial targets, such as the Type-54 Banshee or the Z-1800 Phaeton, but is still easily capable of penetrating their armor.

List of appearances

 * Halo 5: Guardians