SS William A. Irvin is a lake freighter, named for William A. Irvin, that sailed as a bulk freighter on the Great Lakes as part US Steel's lake fleet. She was flagship of the company fleet from her launch in the depths of the Great Depression in 1938 until 1975 and then was a general workhorse of the fleet until her retirement in 1978.

Lake freighters, or lakers, are bulk carrier vessels operating on the Great Lakes of North America. These vessels are traditionally called boats, although classified as ships. Freighters typically have a long, narrow hull, a raised pilothouse, and the engine located at the rear of the ship.