The resulting space savings allowed for reducing the armor's profile without compromising protection. While the T-51 power armor relied on a lightweight poly-laminate composite shell for protection, the advanced model uses lightweight metal alloys as a basis, reinforced with ceramic castings at key points. The X-01 advanced powered infantry combat armor is designed for a single human operator, provided with the comfort and protection of a next-generation suit of armor.

Work on the model was restarted by the Enclave in 2198, although it wasn't until 2215 that the research efforts began in earnest under a presidential mandate, with the first production model created in 2220. It represented a radical, new approach to designing powered armor, eschewing traditional armor design philosophies, but was never deployed in larger quantities until the 23rd century. The first test batch of the armor, designated X-01 Mk I, was developed for presidential bodyguards, and served as the baseline for the remnants of the United States military, who developed it into a power armor tailored for the post-War wasteland.

The development of the first suit of advanced power armor, designated X-01, began shortly before the Great War.

2.5 Advanced power armor Mark II (Tesla variant).

2.3 Advanced power armor Mark I (Tesla variant).

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