The 1947 National Football League season resulted in a tie for the Eastern Division championship between the Philadelphia Eagles and Pittsburgh Steelers, requiring a one-game playoff to be held between them. This division championship game, the Steelers' only playoff appearance of any kind prior to the AFL-NFL merger, was played on December 21, 1947, at Pittsburgh's Forbes Field. The winner of that game then traveled to Chicago to play in the championship game against the Chicago Cardinals on December 28.
References
1947 NFL playoffs Wikipedia(Text) CC BY-SA