Robert H. McDormick; “The Eighteenth St. Sewer Explosion at Detroit;” Engineering News; February 12, 1914; p. 373.
18 Feb 1915 advertisement in Engineering News for a new tunneling machine … for use in clay, stiff sand, and gravel formations. Note that the source of machine’s power is an electric motor. Carpenter Construction Co. Document provided courtesy of Jon Schladweiler