The Soo Line B-4 class were 0-6-0 steam locomotives constructed for the Minneapolis, St. Paul and Sault Ste. Marie Railway (Soo Line) by the American Locomotive Company. Six (#344–349) were built at their Schenectady plant in 1915, with a further five (#350–354) being constructed by their Brooks plant in Dunkirk, New York, in 1920.

They were the last, and largest design of purpose-built switch engines that the Soo Line owned, any heavier switching duties were performed by down-graded 2-8-0 freight engines. All were still on the active roster in May 1953,^[1] but all had been retired by the end December 1954 when the railroad completed its dieselization.

Two are preserved^[2] - #346 from the first batch, which is displayed at the Wheels Across the Prairie Museum at Tracy, Minnesota, as Dakota, Minnesota and Eastern #9, and #353 from the second batch, which is operational and gives free rides annually at the Western Minnesota Steam Thresher's Reunion, Rollag, Minnesota.