Lok Durd, a weapons developer and general in the Separatist army, conceived of the Defoliator as a means of eradicating living troops and terrain while leaving the battle droid forces unscathed. Once detonated, a Defoliator capsule creates a growing radius of destructive energy that scorches all living matter in its path. To launch these specialized warheads, Durd developed the DDT -- the Defoliator deployment tank -- a modified AAT that can support a heavy artillery launcher as its primary turret armament. For increased stabilization, the tanks lower skirt extends further back than a standard AAT, increasing the length of the vehicle to over 12 meters.
The obese Neimoidian general was eager to show off his experimental weapons technology to Count Dooku, and tested the DDT on the unspoiled landscape of Maridun.
The standard Separatist assault tank is the same AAT used by the Trade Federation during the invasion of Naboo. Unlike the DDT, the AAT has an anti-vehicle laser cannon as its primary turret armament.
The innocent and pacifist Lurmen were in the line of fire of Lok Durd's destructive DDT tests. They were faced with the difficult choice of taking up arms to protect their lives, or not arming themselves to protect their ideals.
Tasked by Count Dooku to exact revenge against the Nightsisters of Dathomir, General Grievous unleashed an experimental DDT tank to wipe out the twisted forests used as cover by the wily witches.