During an urban redevelopment project in Gyeonggi Province, workers accidentally discovered a subterranean stone chamber containing a rare naval archive of the Goguryeo Dynasty. The site, dating to the 6th century CE, yielded several dozen inscribed wooden slats that detail the structural designs and iron-reinforcement specifications for a previously unknown class of heavily armored warships.
The blueprints suggest that the Goguryeo navy was experimenting with iron-clad plating and specialized internal ribbing to withstand ramming maneuvers in the turbulent waters of the Yellow Sea. This discovery provides the first physical evidence of a centralized maritime engineering bureau in ancient Korea and suggests that Goguryeo naval technology was far more advanced than previously assumed, potentially influencing later 'turtle ship' designs.