Well, that sure is big, but the 16-inch guns of the Iowa-Class battleships (the Iowa, the Wisconsin, the Missouri, and the New Jersey) were quite a bit bigger (16 inches is 406 mm) and they could project all sorts of ordnance, to include a nuclear projectile, to targets well in excess of 20 + miles....and each ship has 9 of them.
Now THOSE are some guns.
But the Navy only manufactured 50 nuclear rounds. They had approximately the same yield
or 5 kilotons more than the Army. They were not so sure they would work at the velocity of a 16".
So those 50 rounds sat on shore and were never loaded onto an Iowa Class ship nor ever test fired.
Only the Army actually fired a test round.