The armor was created by the Enclave's skilled team of engineers and scientists after the Great War, as a result of a research program initiated in 2198, part of a larger project to develop various technologies. In 2215 the first actually superior suit is manufactured, entering service in 2220. Various accidents involved in its creation were classified by order of the Enclave's President Dick Richardson for the sake of morale amongst the Enclave's personnel.
It is composed of lightweight metal alloys, and reinforced with ceramic castings at key stress points. The motion-assist servo-motors used in the armor appear to be high quality models as well. The suit has an auto-gyro system to keep it upright and the knees can be locked in position, to prevent the wearer from falling over, if, for some reason, he or she loses consciousness on duty (i.e, takes a nap).
Additionally, like the T-51b power armor, it includes a recycling system that can convert human waste into drinkable water, enhancing survival and an air conditioning system for comfort.
It was issued exclusively to Enclave troopers operating on the United States mainland, with the Enclave emblem prominently displayed on the breastplate, while rank indicators were usually painted on the shoulders of the armor.
Secret Service units maintained use of the armor due to the potential for improvement of the mark I's chassis, as well as most of it's soldiers preferring the old air conditioning system and overall comfort-level not seen in the mark II.
Special Agent CRONOS, the Director of the miniscule and fragmented, but effectively reorganized Secret Service that was active during the late 2270's into the early 2290's, had his own suit of advanced power armor mark I he was grafted into retrofitted and hardened to be composed almost entirely of duraframe alloy plating, coupled along with small composite plating additions to the nuclear reactor and cooling unit on the back of it.