Shawmut is a subway station on the Ashmont branch of the MBTA Red Line, located on Dayton Street in Dorchester, Massachusetts. The station, the only underground station on the Red Line south of Andrew, is in a shallow cut-and-cover subway tunnel that runs from Park Street in Dorchester south to Peabody Square where it surfaces at Ashmont. Shawmut opened along with Ashmont on September 1, 1928 as part of a southward extension of the Cambridge-Dorchester Line.HistoryShawmut Branch RailroadIn 1872, the Old Colony Railroad took over the Shawmut Branch Railroad, which branched off the main line at Harrison Square and ran through Dorchester to Milton. The branch line originally included stations at Melville Avenue and Centre Street, just one-quarter mile apart, which were consolidated into Shawmut station in 1884. Shawmut station was located between Mather and Centre streets on the east side of the tracks.The New York, New Haven and Hartford Railroad acquired the Old Colony and took over operations in 1893. In 1924, the Boston Elevated Railway bought the Shawmut Branch Railroad and part of the Milton Branch in preparation for extending the Cambridge-Dorchester Line, although New Haven trains ran on the line until 1926.Rapid transit conversionThe Shawmut Branch reopened as a rapid transit extension in two sections: to Fields Corner (with intermediate stops along the Old Colony mainline at Columbia and Savin Hill) in November 1927, then further to Ashmont with an intermediate stop at Shawmut on September 1, 1928. The Cambridge-Dorchester Line became the Red Line in August 1965.