In I.G.I.-1: I'm Going In (also known as Project I.G.I.), you cannot skip missions or unlock them out of order through a menu option. The game uses a linear, checkpoint-based save system.
: The game will register the mission as successful, returning you to the menu with the next mission now available. 2. Replacing Save Games
Method 2 — Use the Built-in Mission Select (if present)
Paste the following code exactly:
Once unlocked, you will have access to the following 14 missions in order: Military Airbase Radar Base Get Priboi Border Crossing Missile Trainyard Defend Priboi Eagle's Nest I Eagle's Nest II Nuclear Infiltration Finding the Bomb
Replace the existing contents with the downloaded save files.
Project I.G.I. was criticized at launch for its lack of mid-mission saves. If you die near the end of a 40-minute mission, you have to start the entire level from scratch. By unlocking all missions, you can practice later stages, explore the massive open-ended maps, or bypass a "bugged" mission that prevents you from progressing naturally.
Find the line starting with:
MISSION_COMPLETE
Once unlocked, you will have access to these levels in order: Trainyard SAM Base Military Airbase GOD Radar Base Get Priboi Border Crossing Re-Supply Missile Trainyard Defend Priboi Eagle's Nest I Eagle's Nest II Nuclear Infiltration Finding the Bomb