To destroy Metal Gear, you'll need specialized explosives. Your next goal is to find the C4 plastic explosives and the Rocket Launcher. C4 is typically found in a heavily guarded armory or storage facility, often requiring a higher-level Card Key (e.g., Card Key 3 or 4) to access. The Rocket Launcher is usually located in a separate, equally secure area. Consult your radio contacts (Miller, Diane) for hints on their locations.
The path to these items will involve navigating through areas with laser grids, electric floors, and more advanced enemy types, including armored guards. You'll need to find items like the Infrared Goggles to see laser grids and the Bulletproof Vest to mitigate damage. The Rocket Launcher is crucial for dealing with certain bosses and, ultimately, Metal Gear itself. Ensure you have a good supply of ammunition for it.
Remember to use your acquired Card Keys to open doors. Each key corresponds to a specific door level. If a door doesn't open, you likely need a higher-level key. Explore thoroughly and backtrack if necessary to find all required items.