Tank Boat History
The X18 would hardly be the first tank boat. Starting in the 1930s and going into World War II, Soviet Russia experimented with heavier armed river boats, using already-made tank turrets as the turrets for their riverine vessels. Not just experiments, these ships saw battle, participating in fights on the Black Sea and the Baltic sea.
During WWII, the U.S. Navy tried putting tank turrets on landing craft, but found the guns were too heavy and the boat engines too weak. With modern construction techniques, and 70 years of development since, it’s unlikely the X18 will have these problems.