The 600-footers were a class of lake freighters all built to the design of the J. Pierpont Morgan.
[1][2] The J. Pierpont Morgan was launched in April, 1906, and was, at the time, the longest vessel on the Great Lakes.
Mark L. Thompson, author of Queen of the Lakes, wrote that between 56 and 76 vessels were built to this design.
[2] The 600-footers could use harbours that larger 730 feet (220 m) seawaymax vessels can't use.
They were powered by triple expansion steam engines, providing 1,800 shaft horsepower (1,300 kW), and could carry 11,000 tons of cargo.