There are no contemporary Korean sources from Yi Sun-sin's time which refer to the turtle ship as ironclad. Admiral Yi Sun-sin himself makes no mention of such a design in his comprehensive war diary. His nephew Yi Beon, who also witnessed the war and left a historical account of the events, does not mention iron cladding either. The annals of King Seonjo, a many thousand pages long compilation of all kinds of official documents of the period, are also silent on the subject. Prime Minister Ryu Seong-ryong even explicitly described the turtle ship as "covered by wooden planks on top".