Project Icarus was an Armacham Technology Corporation bioengineering research program started in 1973, stemming from studies on microgravity-related health problems.
These problems were best countered with exercise, but NASA wanted their subjects to maintain bone density during periods of both microgravity and stasis. The subjects were strapped down for months at a time and fed a strict diet to maintain their weight. Despite numerous attempts, ATC was initially unable to find a solution for the bone loss.
Icarus scientists then developed a carbon fiber composite that was unaffected by microgravity conditions, but light enough to add negligible weight to an astronaut. The composite was applied to the surface of bones to help prevent density decay, but it was unsuccessful.
ATC then decided to use their newly created Replicas to perform surgery on, removing each bone and replacing it with an exact replica created out of the composite. The surgeries proved successful. Not only did subjects not lose bone density, the light weight of the bone replacements made their speed and dexterity increase to levels never seen in humans before.
Icarus was shut down due to being too expensive in favor of Project Perseus, which was funded by the Department of Defense. As Project Icarus drew to a close, all subjects were placed in containment, later being freed when Fettel went rogue, using his Replicas to release all the test subjects. The Assassins were more than happy to turn on ATC employees to exact their revenge.