As slip-on garments without buttons, the earliest T-shirt dates back to sometime between the 1898 Spanish–American War and 1913, when the U. S. Navy began issuing them as undergarments. These were a crew-necked, short-sleeved, white cotton undershirt to be worn under a uniform. It became common for sailors and Marines in work parties, the early submarines, and tropical climates to remove their uniform jacket, wearing (and soiling) only the undershirt. They soon became popular as a bottom layer of clothing for workers in various industries, including agriculture. The T-shirt was easily fitted, easily cleaned, and inexpensive, and for those reasons, it became the shirt of choice for young boys. Boys' shirts were made in various colors and patterns. The word T-shirt became part of American English by the 1920s, and appeared in the Merriam-Webster Dictionary.