Cathal Joseph Smyth (born 14 January 1959 in Marylebone, London), also known as Chas Smash, is an English musician, best known as the backing singer, trumpet player, harmonica player and dancer in the ska/pop band Madness.
In addition to trumpet, he plays the bass guitar (having initially joined Madness as a bassist), acoustic guitar and other various percussion instruments. He occasionally performs the lead vocals, such as on the songs "Michael Caine", "Wings of a Dove", "One Step Beyond" and "Madness (Is All in the Mind)". He was initially an occasional songwriter, becoming a more regular contributor over the course of Madness's career, and was credited as co-writer on the group's major international hit, "Our House".
In 1976, The North London Invaders recruited the 17-year-old Smyth to play bass until he was replaced in 1977 by Gavin Rogers. Three years later, he became the last of the seven original Madness members to join the band. Prior to that he was a friend of the band and danced onstage at concerts. After Madness broke up in 1986, he formed a new short-lived band The Madness in 1988 along with Suggs, Lee Thompson and Chris Foreman.