Infiltrator is a 1986 flight simulator/spy game by U.S. Gold. During each of the three missions you first have to fly a helicopter to an enemy base, then sneak in and complete an assignment, e.g. retrieve a security card and photograph secret documents, then fly safely back home.
To solve the missions, one first has to
- remember the correct procedures for starting and landing the helicopter.
- in the flight sim part, write down all the call signs and whether they are friend or foe (does not change from game to game).
- in the ground mission part, map out the enemy bases with the locations of all the hidden objects, e.g. janitor's uniform (helps to blend in), security card, weapons caches, etc.
Once that is done, the game instantly goes from very hard to relatively easy and repetitive.