Galaxian3: Project Dragoon is a 3D rail shooter video game developed and published by Namco. It was originally a theme park attraction designed for the International Garden and Greenery Exposition (Expo '90) in Japan, and was later released as an arcade game in 1992. The game involves players controlling a starship named the Dragoon in its mission to destroy Cannon Seed, a superweapon set to destroy what is left of the human race.

An entry in the Galaxian series, Galaxian3 was conceived following Namco's success with motion-based arcade games in the late-1980s, such as Final Lap and Metal Hawk. The attraction version, housed in a massive circular room and supporting 28 players, was designed by company engineer Shigeki Toyama. He was tasked with making the biggest video game possible to prevent other companies from copying it, in addition to creating a game that showed off Namco's 3D technology. The attraction was moved to Namco's Wonder Eggs theme park in 1992, where it remained until its closure in 2000. Namco developed other smaller versions for other theme parks and its own video arcades in Japan and Taiwan. The game saw a home release for the PlayStation in 1996 in Japan and PAL regions titled Galaxian³.

Galaxian3's demonstration at Expo '90 was received favorably, with showgoers showing interest and enthusiasm in the game's 3D flat-shaded graphics and technology. The arcade release was also praised for its technological features and impressiveness, while the PlayStation version saw mixed responses for its outdated gameplay and the appeal of the original having been lost. Galaxian3 has since gained a dedicated following among arcade game collectors for its scarcity, and has also been the focus of video game preservation efforts.

Galaxian3: Project Dragoon is a rail shooter video game. It uses Laserdisc-based video footage with 3D polygonal graphics overlaid on top. Each version supports a varied number of players; for instance, the theme park attraction allows for 28, while the PlayStation version only supports four. In the game, players assume control of the Dragoon, a massive space vessel created by the United Galaxy Space Force (UGSF) to destroy a race of hostile aliens known as the Unknown Intellectual Mechanized Species (UIMS). Players do not control the Dragoon directly, as it moves along a pre-set path; instead, they control a colored cursor that can fire lasers at incoming enemies. The objective is to make it towards the end without getting hit. All players share one health bar, labeled as "ENERGY" and positioned at the bottom of the screen. The meter depletes when the Dragoon is hit by enemies, obstacles, or projectiles.

The story is set far into the future, where mankind is studying interstellar travel and exploring the outer regions of the Solar System. When a group of humans settle on the planet Alpha, they detect unusual crustal movements within its surface. In response, the UGSF is sent to investigate, only to discover the planet is being inhabited by the UIMS. The race is using Alpha to construct a powerful superweapon called Cannon Seed, capable of destroying any planet in its radius. To prevent Cannon Seed from destroying what is left of humanity, the UGSF deploys its largest and most-powerful starship, the Dragoon, to destroy the UIMS once and for all.

During the late 1980s, Japanese video game company Namco began to experiment with making arcade games that felt like miniature theme park attractions, such as sit-down machines like Final Lap (1987), and motion-based games such as Metal Hawk (1988) and Winning Run (1989). Namco had also started opening up large amusement centers across Japan, which featured many of these "taikan" arcade games alongside standard video game cabinets. With the motion games being critically and commercially successful, and the amusement centers turning a high profit, the company started drafting plans for a potential Namco-themed amusement park, with attractions based on their games. Galaxian3 was the first of these attractions to be conceived. Namco planners decided on basic foundations for the game, such as how long a single-play would be and the level structure, before presenting and commissioning the game to engineer Shigeki Toyama, known for his work on Xevious and Point Blank.

Toyama's supervisor instructed him and rest of the development team to pour all of their energy into the project, even if it meant other projects had to be postponed — as such, Namco only produced a small number of games in 1990. The goal of the project was to create the "greatest game in the world", and to make an arcade game so massive that other companies couldn't imitate it, an idea believed to stem from Namco's bitter rivalry with Sega. Executives wanted the game finished in time for the 1990 International Garden and Greenery Exposition, also known as Expo '90, in Osaka, giving Toyama and the production staff a tight deadline.

The game was housed in a large, circular room, with massive curved fiberglass projector screens surrounding it. Players were seated in a large cylindrical device placed in the center of the room, powered by hydraulics and moving around as the game progressed. Dubbed the "Motion Unit", it proved difficult to design during the production phase, as Toyama and others had issues with the hydraulics. The hydraulics themselves were purchased from an outside company instead of being made in-house, however due to them being created by a new hire were full of programming errors. Staff wanted the Motion Unit to have the feeling of a rollercoaster, with swift dives and sharp turns. An emergency stop button was implemented in the event that the Motion Unit would keep moving even when the game ended. Numerous other issues were found as well, such as the wires being too short to let the Motion Unit move and the hardware inside being knocked and jostled around. The game could seat a maximum of 28 players due to the curvature of the fiberglass screens and the design of the room itself; Toyama thought this could help increase the game's appeal, as if they made something that massive other companies wouldn't be able to copy it. Due to its sheer scale, Toyama compared designing the machine to designing a building.