Charlton turned professional in 1920 and first entered the Football League in 1921. Since then the club has had four separate periods in the top flight of English football: 1936–1957, 1986–1990, 1998–1999, and 2000–2007. Historically, Charlton's most successful period was the 1930s, when the club's highest league finishes were recorded, including runners-up of the First Division in 1937. After World War II, Charlton reached two consecutive FA Cup finals, losing in 1946, and winning in 1947.