Warhorse foi uma banda formada pelo ex-baixista do Deep Purple Nick Simper. Ele deixou o Deep Purple em 1969 e juntou-se à banda de Marsha Hunt. Após pouco tempo, Simper substituiu os outros músicos de sua banda de apoio por Ged Peck na guitarra e Mac Poole na bateria. Enquanto isso acontecia, Simper continuava a tocar em um projeto paralelo juntamente com Peck, Poole e o vocalista Ashley Holt.
The band began to tour, but made little progress, and the album failed to chart. A single, "St. Louis", was also released, which also failed to chart. By 1971, after arguments about style, Peck left and moved to classical guitar playing. He was replaced by Pete Parks.
In June 1972, their next album Red Sea was released, but soon after its release, Warhorse were dropped from the label. Around the same time, Poole decided to leave Warhorse, for Gong. The band carried on, and replaced Poole with Barney James. Wakeman used both Holt and James for his solo album, Journey to the Centre of the Earth. Warhorse's last concert in 1974 was at Polhill College, Bedford.
Warhorse musicians (Holt, Parks, Simper, Wilson, and Poole) have since played together on occasions, including 1985 and 2005; latterly for drummer Mac Poole's 60th birthday.