Near the Port Huron Amtrak station is the St. Clair Tunnel. This is the train tunnel that connects Port Huron to Sarnia.
The tunnel was designed by Joseph Hobson and was a little over 6000 feet long. Many new techniques were developed in constructing this tunnel.
Apparently, there was an attempt to sabotage this during World War I.
After World War II, train cars started to get larger and Canadian National (which took over the Grand Trunk) was forced to use ferries again. It wasn't until the 1990's that the current larger tunnel was built.