Great Lakes Harbors Study--second Interim Report on Duluth-Superior Harbor, Minnesota and Wisconsin: Letter from the Secretary of the Army Transmitting a Letter from the Chief of Engineers, Dept. of the Army, Dated May 29, 1959, Submitting a Report...requested by the Resolutions of the Committees on Public Works, United States Senate and House of Representatives, Adopted May 18, 1956, June 27, 1956, July 13, 1949, and June 29, 1955