After rescuing Dr. Kio Marv (or attempting to), your ultimate objective shifts to neutralizing Metal Gear D, the bipedal nuclear-armed tank. This will involve infiltrating the deepest parts of the Zanzibar Land fortress, often requiring you to acquire specialized weapons or equipment to damage the Metal Gear. You'll face increasingly difficult security, including advanced security cameras, infrared sensors, and heavily armed guards. The path to Metal Gear D is a gauntlet, testing all your stealth and combat skills. Be prepared for multiple boss encounters leading up to the final confrontation. You'll need to gather information about Metal Gear D's weaknesses, often through Codec calls or by finding documents within the base. Stock up on rations and ammunition before proceeding to the final areas.
