The St. Clair Tunnel
The first international submarine railway tunnel in North America was built here, 1889-9, by the Grand Trunk Railway Company of Canada. It connects Sarnia with Port Huron, Michigan. To compete with U.S. railways for the lucrative Chicago and mid-western freight and passenger traffic, the Grand Trunk required uninterrupted access to these areas. A ferry service across the St. Clair was considered unsatisfactory and a bridge impracticable. The tunnel and its approaches, over 3 km long and including 1837 m of iron tube, were built under the direction of Joseph Hobson. Electrification of the line through the tunnel was completed in 1908 and remained until the introduction of diesel trains.
Plaque via Alan L. Brown's site Ontario Plaques. Full page here.