The history of the American T-shirt goes back to World War I when American troops noticed European soldiers wearing a comfortable,light cotton undershirt during the hot and humid summer day.The European soldiers dealt with the heat by stripping off to their undershirts while the American soldiers stifled in their hot woolen uniforms.The undershirts quickly caught on with the American.The"T-shirt"got its name because of its simple design resembling the letter T.