The Watertown Subdivision or Watertown Sub is a 92.7-mile (149.2 km) railway line in Wisconsin operated by Canadian Pacific Kansas City (CPKC) through its primary United States subsidiary, the Soo Line Railroad. It meets CPKC's Tomah Subdivision in the west in Portage and runs to Milwaukee in the east where it meets the C&M Subdivision. The Watertown Subdivision had previously been operated by the Chicago, Milwaukee, St. Paul and Pacific Railroad, though the Soo Line Railroad took it over when the Milwaukee Road folded. Canadian Pacific gained ownership via taking over the Soo Line. CP consolidated its operations with the Kansas City Southern Railway on April 14, 2023 to form CPKC.

The Chicago and Milwaukee Subdivision is a 85.5-mile (137.6 km) railway line running between Chicago, Illinois and Milwaukee, Wisconsin. It is mostly dispatched by Canadian Pacific Kansas City Limited from a CP Rail facility in Minneapolis. From Pacific Junction to Chicago Union Station, it is dispatched by Metra's Consolidated Control Facility. The C&M Subdivision is the primary of CPKC's two northern routes from Chicago. The Union Pacific Railroad operates its Milwaukee Subdivision, a former Chicago & Northwestern Railway line, parallel to the C&M.