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 undershirt while american soldiers stifled in their wool uniforms. the undershirt 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.