Developed by the U.S. Navy weapons station at Newport, Rhode Island, the Mk XIII served as the United States' standard aerial torpedo in World War II. Thirteen feet long and 22.4 inches in diameter, a combat-ready Mk XIII weighed about 2,200 lbs, including 600 lbs of Torpex high explosive. In the water, it traveled at 33.5 knots (39 mph) to a maximum distance of 6,300 yards, and the flow of water turned an impeller beneath the nose, which armed the firing mechanism. Other countries' aerial torpedoes tended to be smaller and lighter than the Mk XIII, allowing them to be dropped at a higher altitude and airspeed. If dropped from a height of greater than 50 feet or at an airspeed faster than 110 knots (126 mph), the early versions of the Mk XIII tended to break up.