of turtle ships in battle, as well as the testing of weaponry used in the ships. The mounted weapons, Korean cannons with ranges from about 300 to 500 metres, were tested on March 12, 1592. Yi completed his first turtle ship and launched it on March 27, 1592, one day before the Siege of Busanjin and the Battle of Dadaejin. It is unknown precisely how many of Admiral Yi's Turtle Ships were constructed. The cost of one of these armored warships would have been high, especially if the deck was lined with hexagonal iron plates as some sources suggest. Structure Many different versions of the turtle ships served during the war, but in general they were about long, and strongly resembled the panokseon's bottom structure. The turtle ship was technically a hull that was placed on top of a panokseon with a large anchor held in the front of the ship and other minor modifications. On the bow of the vessel was mounted a dragon head which emitted sulfur smoke to effectively hide its movement from the enemy in short distance combat. The dragon head, which is considered the most distinguishing feature of the vessel, was large enough for a cannon to fit inside. The dragon head served as a form of psychological warfare, with the aim of striking fear to the enemy. Early versions of the turtle ship would burn poisonous materials in the dragon's head to release a poisonous smoke. In the front of the ship was a large anchor. Below the anchor was a wooden crest that was shaped like a face, and these were used to ram into enemy ships. Similar to the standard panokseon, the turtle ship had two masts and two sails. Oars were also used for maneuvering and increased speed. Another advantage the turtle ship had was that it could turn on its own radius. The turtle ship had 10 oars and 11 cannon portholes on each side. Usually, there was one cannon porthole in the dragon head's mouth. There were two more cannon portholes on the front and back of the turtle ship. The heavy cannons enabled the turtle ships to unleash a mass volley of cannonballs (some would use special wooden bolts several feet in length, with specially engineered iron fins). Its crew complement usually comprised about 50 to 60 fighting marines and 70 oarsmen, as well as the captain. Sources