The T51 power armor series was the pinnacle of mechanized protection before the Great War, providing a valuable balance of protection and mobility. Formally designated Powered Infantry Armor Model T51, it was created by West Tek under contract from the United States government, and represented the company's single largest contract.

It is also the very first type of power armor introduced in the Fallout series, prominently displayed on the cover of the first game, and featuring in virtually every game since.