The Modular Atomic Disintegrator is a wonder weapon featured in the Call of Duty: Infinite Warfare Zombies map Attack of the Radioactive Thing. It shoots extremely powerful atomic blasts at zombies. It can only be obtained through the Magic Wheel and can only be upgraded with parts found around the map.
By grabbing the crowbar melee weapon from the small room near Bombstoppers, you simply hit three control panels around the map with it to get the parts for the M.A.D.
The Crank is in the control panel just outside the movie studio near Magic Wheel spawn. When added, the player can hold the ADS button to charge the M.A.D. up for a more powerful shot, which uses 5 rounds at once.
The Grip panel is found in the trailer park next to the entrance to the men's bathroom. When added, the recoil is reduced and more range is added.
The Plunger part is found in the panel in the alleyway behind the blue truck parked near the gas station. When added, the M.A.D.'s ammo can be refilled using radioactive eggs spawning around the map.