One of the longest-running groups in country music, the Oak Ridge Boys started life as a gospel quartet before gradually modernizing their style and moving into secular country-pop. Yet even at the height of their popularity in the late '70s and early '80s -- when they were big enough to cross over to the pop charts -- their sound always remained deeply rooted in country gospel harmony. Their existence dates all the way back to World War II, circa 1942-1943, when a Knoxville, TN, group began performing gospel songs in nearby Oak Ridge, the home of an atomic bomb research facility.