After brief trial runs with Larry Wallis (February – October 1972) and Bernie Marsden (who toured with UFO in Europe and recorded a pair of demos, "Oh My" and "Sixteen") the band recruited Michael Schenker from the Scorpions in June 1973. Schenker was only 18 at the time but was already a well-respected guitarist. On a new label, Chrysalis Records, the revamped UFO recorded a non-LP single in 1973, "Give Her The Gun" and "Sweet Little Thing" with producer Derek Lawrence. In 1974, under producer Leo Lyons (formerly of Ten Years After), UFO recorded "Phenomenon", which highlighted the band's harder-edged guitar sound. "Phenomenon" contains many fan favourites such as "Doctor Doctor" (later a minor hit single as a live track) and "Rock Bottom" (which was extended live to provide a showcase for Schenker). By the time of the "Phenomenon" tour, ex-Skid Row guitarist Paul "Tonka" Chapman joined the group, but he left in January 1975 to form Lone Star.