Infiltrator

User summary, (details from Wikipedia):

Infiltrator is a rather unique game from 1986 developped for several 8-bit systems. The player takes the role of James "Jimbo" McGibbits, whose mission is to first fly a helicopter to an enemy base, and proceed to infiltrate the base, searching the rooms and drawers for security keys that unlock the doors that block the way to the mission objective.

During the flights to the mission objective, he is interrogated by other aircraft trying to determine if he's friend or foe. A wrong reply causes the enemy to attack, and James then have to engage in air-to-air combat.

James has no weapons for the infiltration missions, but carries false papers that may fool guards if they come close and ask for identification. James also has a limited supply of sleeping spray and gas grenades to knock out guards. If a guard asks for identification and James runs away, the alarm goes, the mission has failed and James need to return to his helicopter to fly home, unless he can shut the alarm off. On certain levels, James can find a janitor dress, which will allow him to sneak into places and fiddle around without the guards getting suspicious.

The game consists of three missions to complete, three flights and three infiltrations. The combination of two game modes and the sneaking and infiltration aspect makes Infiltrator a game far before its time.

Source: Wikipedia, "Infiltrator," available under the CC-BY-SA License.