Moonshine smuggling sub, 1920s, Mississippi
Since time immemorial people have sought to smuggle illicit goods for financial gain. This includes particularly clever people who construct specialized boats or submarines. These contraptions are, by their nature, fascinating irrespective of the contraband involved. Often the line between engineering genius and suicidal nut job is very close. So these craft have a few design surprises in store. Today this is the Narco Sub phenomenon; during the 1920-33 prohibition era cunning individuals devised contraptions to smuggle 'moonshine' whisky from their illicit distilleries to the big cities. Some of these were ‘moonshine submarines’.
Original artwork - CLICK for HIGH-RESOLUTION image. 
Today only one example survives, preserved at the Grand Gulf Military Monument in Vicksburg, Mississippi. Like most ‘narco-submarines’ today this was not a true submarine. Instead it was a low profile boat (LPV), designed to be small and ride low in the water so that the government agents from the Bureau of Prohibition wouldn’t detect it.
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Much of the insides have been long-since been removed, and it’s lost its roof and hydroplanes. But by pouring over photographs, (no small thanks to several people who have helped me with close-up photos and observations) I have been able to reverse-engineer it on paper. The attached cutaway is a reasonable guess of how it would have looked, and how it was laid out inside. Some aspects are imprecise. Any corrections welcome.
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Other sneaky waterborne bootlegers from the prohibition era
Most bootleggers, when they did use boats, kept it simple. Speedboats were used, particularly across the Great Lakes from Canada. One trick was to use a small dingy with a plug at the bottom so that it could be sunk when the Federal agents arrived. The payload would later be salvaged by free diving.
Another trick was to tow containers under or behind a host vessel, very like today’s narco-torpedoes. These could be supplied with compressed air from the towing ship to control their buoyancy. And they could be marked by a piece of wood floating on the surface if they had to be cut loose. Similar 'torpedoes' were employed in an underwater conveyor belt system, across the water border from Canada.
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