Judas Priest were one of the first heavy metal bands to modernize the twin-guitar sound, with the duo of K. K. Downing and Glenn Tipton. They combined this sound with Rob Halford's unique vocal style to create their own distinctive style of heavy-rock. They are cited often for their influence on the rock music sub-genre, heavy metal. Many people, including influential musicians and members of prominent hard rock and heavy metal bands, believe that among the foundations for what would define "pure" heavy metal were three early Judas Priest albums: Sad Wings of Destiny (1976), Sin After Sin (1977), and Stained Class (1978). The band often played faster than most rock groups of the time and brought a more "metallic" sound to the guitars. The songs varied from simple and straightforward tunes (e.g. "Starbreaker") to fairly structured material, changing from fast and loud to slower tempo and softer tunes in one song (e.g., "Victim of Changes", "Run of the Mill", "Beyond the Realms of Death"). Some songs, such as 1978's "Exciter", were groundbreaking for their sheer ferocity and speed; few, if any, bands excepting Motorhead, played with the same tempo. Other songs, like "Dissident Aggressor", "Sinner" and "Tyrant", are considered to be the heaviest songs of their day, and today are considered classic metal tracks. Their 1978 album Killing Machine (retitled Hell Bent for Leather and released in 1979 in the USA) saw a change of direction towards shorter, poppier, more American-influenced songs. The following release, British Steel (14 April 1980), took an even sharper turn in the same direction and was perhaps the first heavy metal album to record radio-friendly songs with pop hooks, in a concise format. The band's next effort, Point of Entry (26 February 1981), is harder to define — the sound was very "raw" (i.e. minimal sound manipulation) and the songs were somewhat moody, and paced at a slower than usual tempo. As guitarist Glenn Tipton later admitted, Point of Entry had the tough task of living up to the standards set by its predecessor, and failed to do so. Subsequent albums Screaming for Vengeance (17 July 1982), which contained the popular radio hit "You've Got Another Thing Comin'", and Defenders of the Faith (4 January 1984) once again set high standards in intensity and production, and continued to influence the sonic shape of heavy metal. Turbo (15 April 1986) found the group introducing a "synth-guitar" sound to their metal template. TOURS; Judas Priest Tour 1969 The return of the Priest tour 1970-1971 (First gig of the tour with Black Sabbath) Whiskey Woman Tour 1972 Never Turn Your Back On A Friend Tour 1973 (First Tour with Rob Halford, Judas Priest is the support act of Budgie) Gull Record Tour 1974 (First Tour with Glenn Tipton, Judas Priest is the support act of Budgie again) Rocka Rolla Tour 1974 Sad Wings Of Destiny Tour 1975-1976 Sin After Sin Tour 1977 Stained Class Tour 1978 Killing Machine Tour 1978 Killing Machine/Hell Bent For Leather Tour 1979 British Steel Tour 1980 World Wide Blitz Tour 1981 World Vengeance Tour 1982-1983 Metal Conqueror Tour 1984 Live Aid 1985 Fuel For Life Tour 1986 Mercenaries Of Metal Tour 1988 Painkiller Tour 1990 Operation Rock 'N' Roll Tour 1991 Jugulator World Tour 1998 Demolition World Tour 2001-2002 Reunited Summer Tour 2004 Ozzfest Tour 2004 Retribution World Tour 2004-2005 2008/2009 World Tour 2008-2009 Epitaph World Tour 2011-2012