Corridor 7: Alien Invasion

The player takes control of the lone soldier who has infiltrated the alien invaded military base. Like all first-person shooters, the game is rendered from the player's perspective. Corridor 7 is not organized in episodes. Instead, there are 30 (floppy disk version) or 40 (CD version) levels to explore plus 6 more bonus levels. The gameplay slightly differs from that of most FPS games because the player, rather than finding an exit surviving the various enemies scattered around, is tasked with the duty of killing the aliens present on the level. Once this objective is achieved he will be granted access to the next floor of the base through a lift which is also the starting point of each level. The skill setting selected when starting the game influences the percentage of aliens that need to be eliminated:

Corporal: the levels contain few aliens and only 10% kills are required to gain access of the elevator.
Lieutenant: the aliens increase in number and 75% kills are required.
Captain: this is the standard difficulty setting and requires that 100% of the aliens are killed.
Major: like Captain, but with a higher number of enemies.
President: like Major, but features a randomization factor which scatters around the level all the objects present. This setting is only available in the CD version.

To help hunting down the aliens the player can activate the proximity map in one corner of the screen. This function shows a small section of the current level with all active aliens as yellow blips and can be expanded by finding the floor plan. Upon collecting this object the proximity map is extended to show the whole level and the position of every alien.

Corridor 7 levels can be split into different blocks depending on their setting. The first twenty levels of Delta Base comprise a mix of offices, research labs, computer rooms and storage warehouses themed with appropriate decorations and furniture. Next comes the so called alien converted floors: these 10 levels of Delta Base have been completely reorganized by the aliens who brought in their own devices and structures. The converted floors feature a darker light setting and the almost complete disappearance of human made equipment. A third section is made up by the six bonus levels accessible on specific levels throughout Delta Base using an alternate elevator. Such elevator is usually guarded by an alien boss. The total of these 36 levels makes up the original floppy disk release of the game. This version of Corridor 7 ends when the player destroys the Vortex on level 30. The CD version features 10 more levels: rather than destroying the Vortex the player walks through it to reach the aliens' homeworld. The alien levels share some similarities with the alien converted floors, but the major difference is that no kill percentage is required to move on, but an exit teleporter must be found.

There are some more differences from other Wolfenstein 3D engine based games: for instance the player is equipped with a visor capable of both infrared and night vision. Infrared is employed to detect invisible, energy draining force fields or other threats, while night vision is especially useful to better see when playing on dark levels. Ammunition and health are not scattered around the levels as objects to pick up, but rather as dispenser bays encased in the level walls. Health is also available in special rooms called "health chambers" where the player can obtain up to 100 hit points. Corridor 7 features two distinct ammo types as well: the projectiles dispensed from the bays are used to feed all human weapons while energy packs are available to power up the alien guns.

Locked areas do not require a key to be opened, but a color coded (blue or red) passcard is necessary. These cards are granted by operating special wall-sized computer terminals; since these terminals are also placed behind the color coded doors, sometimes it is possible to lure an alien into opening such doors and, after dispatching the creature, quickly move in to get the access without having to wander around in search for another terminal.