An underwater tale of two cities

With the auto industry booming and with Detroit’s population surging in the 1920s, we needed a way to get people and car parts back and forth between Detroit and Windsor.  The solution: dig a massive trench beneath the Detroit River current, drop massive concrete tubes into the trench, and drain 'them. What could possibly go wrong? The Detroit History Podcast story of that civil engineering achievement includes an audio bonus: on a quiet night, you can hear freighters passing overhead.