A project which grew out of the ARPA support for Multics and the sale of Multics systems to the US Air Force. The USAF wanted a system that could be used to handle more than one security classification of data at a time. They contracted with Honeywell and MITRE Corporation to figure out how to do this. Project Guardian led to the creation of the Access Isolation Mechanism, the forerunner of the B2 labeling and star property support in Multics. The DoD Orange Book was influenced by the experience in building secure systems gained in Project Guardian.