"Manhattan" project was the code name for the original XBox.

At the time Japan dominated video consoles with the last western attempt being the disaster which was the 3DO. Thus Microsoft was going "nuke the japanese industry" and gain a foothold.

For further irony the Xbox was in effect was a spiritual successor to Sega's Dreamcast. That Microsoft went with such a distasteful name despite partnering with Sega highlights their cultural issues. Issues which have continued to prevent Xbox from building relationships with Japanese studios.