the history of the american t-shirt goes back to world war i when american troops noticed European soldiers wearing a comfortable, lightweight cotton undershirt during the hot and humid summer days. the European soldiers dealt with the heat by stripping off to their undershirts while american soldiers stifled in their woolen uniforms. the undershirts quickly caught on with the american. because of their simple design, these shirts became known in the U..S. as "T" shirts or "T-shirt.