c. 1912; Addressed to: M. Coppius; "The Detroit River Tunnel has the unique distinction of being the only tunnel of this type ever built. It was constructed in sections, all work being done from the surface of the water without the use of compressed air. The tunnel is operated electrically. Construction was started October 1, 1906, and completed July 1, 1910. The length from portal to portal is 1 3/8 miles and from summit of grade 2 1/2 miles. It was built for the M.C.R.R. at a cost of $8,500,000."