In June 1979, there was news that over sixty sheets of old naval documents had been recovered from an old house in the city of Tongyŏng by an antiquarian. These document sheets were being used as wallpapers in the old house. No systematic information directly related to the studies on the Yi Sun-Sin's turtle-boats(1592-1597) was discovered in the sheets. The author's former work titled "Supplementary Remarks on the Iron-armour-clad of Admiral Yi Sun-Sin's Combat Turtle-boats" briefly introduces the only sheet with records of the length of the vessel's bottom plates and the height of the turtle-boat. This work was published in the Journal of the Korean History of Science Society Vol. 4 No. 1 (1982). Confronted with these scattered document sheets, the first task was to confirm the date of issue of each sheet or bundle of similar records to classify the sources in chronological order. However, except for a document on the crew assignment record for a turtle boat corresponding to year 1592, the dates of issue for other documents were indicated using Kanji(干支: date or year termed in sexagenary cycle) and the corresponding years could not be uniquely determined. However, the dates may be surmised by critically analyzing specific items such as the length of the bottom plates for turtle-boat or battle-ship, and the types of firing arms appearing frequently in the records. The old documents concerning the turtle-boat and the special battle-ship are surmised to be issued over a period of two years starting at 60 years, for the early estimate, or 120 years after the end of the Japanese invasion of 1592-1598. The records on firing arms confirm that the shipboard weapons systems were gradually replaced by the systems equipped with lighter guns in the same period.