The Digital Leap

In the early 1970s, arcades up to that point were run by games that were mainly mechanical or electro-mechanical, such as pinball machines. But with the advent of microprocessors a few years prior, pinball machines have been able to become more sophisticated and have more advanced objectives and whatnot. Video arcade games, which have only existed since the start of the decade, have also been able to evolve with the invention of CPUs. Until then, these machines were comprised of transistor-transistor logic chips or other components that didn't allow for complex games at all. One relatively new amusement machine manufacturer called Magnetic Corporation of America, made their very first arcade game called Paddle-Ball in 1973. If the name didn't give it away, it's entirely a clone of Atari's Pong. The next year, the company reincorporated as Williams Electronics. For whatever reason, they decided to just stick with pinball games for the rest of the decade. It wasn't until the early 1980s that they revisited video arcade games when those by Nintendo, Namco, others by Atari, and Taito inspired them to get a piece of market share.

Finite Territory

The company chose pinball programmer Eugene Jarvis to lead development of the game, assisted by Larry DeMar, Sam Dicker, and Paul Dussault. As this staff was small and inexperienced in the use of technology for electronic game development, they were encouraged to be creative.
The original plan for Williams Electronics' first game was to create a version of Space Invaders with some new features. When this didn't work out due to lacking enjoyment, they shifted to a color version of Asteroids. But because the hardware they were using worked with pixel-based "raster" graphics and also lacked enjoyment, they abandoned their attempt at pixelated Asteroids as well. That's when the team decided to create a new and original game.
As the developers thought about what made Asteroids stand out, they cited the element of wraparound. As the game defined it, this is where the player can move through one extreme of the screen and reappear from the opposite. For their new game, they made it so the game world is larger than the screen could show at once. This meant making it so the player could fly infinitely in one direction, cycling through the environment time and time again horiztonally. Jarvis believed the screen should only scroll left to right, and that's when another employee named Steve Ritchie chimed in, saying the player ought to be able to fly in either direction.

Passive And Aggressive

Six months into development, Williams didn't feel like they were getting anywhere. After researching other arcade games, it was surmised that survival was an important aspect. But, Jarvis wanted lots of action and for there to be a concrete objective to the game, besides survival. So they added astronauts to the ground for the player to defend and to cater to the space theme. When the team added a planetscape to the bottom of the screen, it was only a pixel thick due to hardware limitations not allowing anything more sophisticated.
The enemies were also a big point of Defender's development. There were landers, which were programmed to come down to the bottom and capture the astronauts, then consume them to become a new enemy called a mutant, which charged, fired, and descended upon the player in this state. This resulted in a risk-and-reward element in rescuing the astronauts before the landers can get to them, earning the player a bonus depending on how many are left when all landers are destroyed. Jarvis felt this would encourage players to continue playing. The element of making a "comeback" from a dire situation was applied to the planet as well. "Bombers", enemies which release floating bombs on the screen, were added next. Over time, more enemies were added to create extra gameplay elements. "Swarmers" and "Pods" were designed to attack the player. "Baiters" were included to add pressure and implore the player to complete the level quickly. Each enemy quickly follows the spaceship to collide with it.

Landing Time

In September 1980, Defender was shown off at the American & Music Operators Association, where it got little attention by patrons. Eugene Jarvis believes its complexity may have scared people off at first. However, when it was playtested at arcades, it attracted decent-sized crowds. It was released on November 10, becoming so popular that it sold over 55,000 units and grossed over a billion dollars (with a "B") worldwide! Some say it outperformed Namco's contemporary Pac-Man.