In 1974, the Cocoon was assigned to defend the entrance to the Peace Sentinels' Mine Base from the MSF (,Militaires Sans Frontières). The Cocoon arrived just seconds after Snake managed to defeat twelve sniper units that were guarding the facility's cargo elevator. Despite it's lack of mobility, the Cocoon proved to be a powerful weapon with it's turrets, missles, and cannon. Snake managed to decommission it for good after dealing enough damage and taking out the memory boards in the AI pod. Because of its decommissioning, the security panel of the doorway to the Mine Base's interior also ended up damaged due to some of Cocoon's fragments of armor smashing into it. allowing Snake to enter in the base.
Over 50 Mini-Machineguns, 6 Miniguns/Turrets, An Arm with sawblade and turret, A Large caliber cannon, and treads
The Cocoon is proven to be the biggest machine in Metal Gear Solid Peace Walker.