Years ago, I asked Unca Cecil about the Mystery Submarine found in Lake Michigan & nearby waters. Sadly, the original column may not be online anymore. 
But I have also heard that yet another mystery submarine may have been located!
Wassup with the submarines?
Is Aquaman opening a driving school? {Heh. “School”.}
Hey! Long time no see/hear/read/whatever!
I remember that column from years ago. Somehow it was teasered on Google News and after reading the article I found that the link at the bottom brought me here.
I participated quite enthusiastically for a while and then got swamped with administrative duties at my work.
It’s great to see you’re still around, great to see he’s coming back, and it’s great to be wandering through again.
–G!
I’m a 99er here. 
Are you talking about the German WWI U-boat sunk 20 miles off Highland Park, IL?
There were several subs found.
Bump.
Someone I know pretty well has been writing extensively about the “Foolkiller”. That one, at least, was “solved” in 2022 and wasn’t a submarine at all, it was an experimental lifeboat. I asked about recent updates and got:
Working on a book, actually! Spoiler: Cecil Adams was right from the very start, naturally. It was always a hoax.
There was also the Tym Barge, a WW2 project, but that was relocated and apparently destroyed quickly by water action: https://news.wttw.com/2014/09/10/ask-geoffrey-910
So my new favourite podcast has being going deeeeeep into this. The Constant:
He did seven 1-2 hour podcasts on the foolkiller.
He originally came to the conclusion it was a submarine invented by Louis Gathmann, eccentric Chicago inventor. But then (after being sent a magazine article about it from 1906) changed his conclusion, and decided it was in fact not a submarine but a lifeboat.
There were 28 subs built Manitowoc Shipbuilding Company during WWII. They performed their trials in Lake Michigan. After that they sailed to Chicago and were put on dry docks and tugged to New Orleans. Link: HOW MANITOWOC-BUILT SUBMARINES REACHED THE SEA