I have enjoyed more than a few...
Where did the name U-Boat come from? The Original Italian U-Boat was a successful submarine sandwich restaurant in Chicago that swelled from a single location in 1975 to 32 stores in its heyday, only to file for bankruptcy and close during the recession in 1983. Chicagoans remember it fondly, according to this article. There isn’t a recipe for their U-Boat Sub online, although it may exist in someone’s attic. The Grill-Meister’s U-Boat is similar to recipes for an Italian Sub, although it has a German spin with the Black Forest ham and garlic bologna.
https://glovergardens.com/2017/03/big-food-for-good-times-the-u-boat-sub/