After deregulation, Denver's four major airlines developed hubs at Stapleton. United occupied Concourse B, Continental and Western occupied Concourse C and Frontier occupied Concourse D. Western flew nonstop between Denver and London in 1981 and 1982, but then shifted resources to Salt Lake City and Los Angeles; Denver had ceased to be a Western hub by the time Delta acquired them in 1987. In 1983 Arrow Air introduced brief transatlantic services to London and Manchester, and Condor flew a weekly charter to Frankfurt, Germany. Southwest Airlines and People Express tried low-cost service to Denver in the mid-1980s, but Southwest withdrew and People Express was acquired by Continental.