indicate that sharp iron spikes protruded from hexagonal plates covering the top of the turtle ship. An advantage of the closed deck was that it protected the Korean sailors and marines from small arms and incendiary fire. The spikes discouraged Japanese from engaging in their primary method of naval combat at the time, grappling an enemy ship with hooks and then boarding it to engage in hand-to-hand combat. Korean written descriptions all point to a maneuverable ship, capable of sudden bursts of speed. Like the panokseon, the turtle ship featured a U-shaped hull which gave it the advantage of a more stable cannon-firing platform, and this ability to turn within its own radius was useful to attack enemies by spinning at the same spot using cannons mounted on the four sides of the turtle ship as cannons in those days took considerable time after firing and before cooling and reloading. The main disadvantage of a U-shaped bottom versus a V-shaped bottom was a somewhat slower cruising speed. Later Turtle Ships held some structural changes as opposed to earlier versions. For example, later iterations of the Turtle Ship had a higher bulwark height. This alteration in the design was made so that more bulwark slots could be added. In turn, these slots could be used for additional weaponry or ventilation for the vessel's occupants. Early illustrations also show initial versions of the ship consisting of overlapping planks on the deck structure, while later depictions show the deck of the vessel covered with flush, hexagonal plates made of wood or iron. Nonetheless, in both earlier and later versions, the Turtle Ship was designed to be surprisingly fast, as it was both oar and sail-powered. Decking There are sources that state that the turtle ship was covered with metal plates, making the first known ship of this kind in history. Sources that question claims of iron plating also exist. While it is clear from the available sources that the roof of the ship was covered with iron spikes to prevent boarding, there is split opinion among historians on whether the turtle ship was iron clad. One Japanese chronicle mentions a clash in August 1592 which involved three Korean turtle ships "covered in iron." However, according to Samuel Hawley, this phrase does not necessarily indicate that Koreans covered the vessels with iron plates; it could refer to the iron spikes protruding from their roofs,