Defender

Defender is an action game originally released in arcades in 1981 by Williams Electronics and later ported to numerous home computers and consoles. The game is a horizontally scrolling shooter where players control a ship with the goal of defending humanoids in a city from the numerous attackers. Defender is often considered one of the most difficult arcade games developed, however the arcade version still went on to sell over 55,000 units making it Williams best selling game as well as one of the highest grossing games of all time. A sequel, Stargate, was released the following year.

The game screen in Defender consists of an area that scrolls horizontally with a city at the bottom of the screen populated by numerous humanoids; most versions of the game depict the city with a single line (a style originally implemented due to hardware limitations), though some versions (such as the Atari 2600 version) vary and use other styles. Players control a spaceship which can fly both left and right (if the end of the gameplay area is reached the screen wraps around to the opposite side). The ship has three defenses; it can fire in the direction the player is facing, use smart bombs, or enter hyperspace to instantly transport to a random location in the city. Smart bombs destroy all oponents that are on the screen; they are limited in number, however additional smart bombs can be gained by scoring enough points. The use of hyperspace can be risky; there is no guarantee the ship won't be warped right on top of an invader destroying it. To help, the very top of the game screen includes a scanner showing the entire city which includes where the player is along with all of the invaders and humanoids.

On each level in the game numerous alien invaders appear and players need to destroy them all in order to proceed to the next, more difficult level. If the players ship comes into contact with any of the invaders or their projectiles, a life is lost; the game ends when players have no more remaining lives. The enemy invaders come in several varieties; while most of the invaders attack only the player, each level includes numerous landers which can also capture the humanoids. If a captured humanoid is carried up to the top of the screen, it is transformed into a dangerous mutant; if all humanoids are captured or destroyed, the entire city is destroyed (this doesn't end the game, but it causes additional mutants to appear and attack making the game more difficult than it already is). Players can rescue captured humanoids by shooting the lander carrying it; if the humanoid is too high off of the ground, players also need to capture the falling humanoid and safely carry it to the ground. At any time players also need to be careful not to shoot the humanoids themselves!

The following types of invaders are encountered in Defender:

• Lander: Landers appear on every level and attempt to capture humanoids; if they carry a humanoid to the top of the screen, it will be transformed into a mutant.
• Bomber: Bombers travel about the city and leave a trail of stationary mines behind. The mines can't be destroyed so players must avoid them.
• Pod: Pods float around the screen randomly starting on the second level. Each pod consists of multiple Swarmers; when a pod is shot, the swarmers are released and rapidly attack the player.
• Swarmer: Swarmers are contained in pods and released when a pod is destroyed; they tend to track the player closely.
• Baiter: Baiters are large ships that move very fast; they usually appear if a player takes too long to complete a level.
• Mutant: Mutants are formed when a humanoid is captured by a lander and carried to the top of the screen or if the city is destroyed. Mutants move sporadically and shoot numerous projectiles at the player making them difficult to destroy.

Points are earned for each alien that is destroyed, for each humanoid that is still alive when a level is completed, and for humanoids that are rescued after being captured. Extra lives are awarded after certain scores are achieved (the number of points required can vary by version or difficulty settings).