Martin introduced the 0-18T tenor guitar in the late 1920s. At this time banjos were a popular rhythm instrument because they were loud enough to be heard over the other dance band instruments. Tenor guitars were aimed at banjoists who wanted to switch to guitar - they had four strings and the same tuning as a banjo but sounded like a guitar. The 0-18T even had banjo tuners for the first couple of years of production. The 0-18T remained in prodcution until 1994 although in later years it was made to order only.