A Cannon in Marine City

My next stop was in Marine City.  We dilly dallied too long in Port Huron to catch the Blough in St. Clair although we didn't miss her by much.  So I figured I would head up the road a bit and catch her in Marine City.

As I was waiting for the Blough, I saw this cannon and took a picture of it.  It looks like it may be a 5 inch deck gun from a submarine but I'm not sure.