First International Tunnel
At this point the Grand Trunk Western Railroad tunnel, linking Port Huron with Canada, passes underneath Gratiot Avenue. This international submarine railway tunnel—first in the world—was opened in 1891. The tunnel’s total length is 11,725 feet, with 2,290 feet underwater. The tunnel operations were electrified in 1908 and completely dieselized in 1958. Tracks were lowered in 1949 to accommodate larger freight cars. During World War I, a plot to blast the tunnel was foiled.
Plaque via Michigan History Center