The action came about six weeks into the war, although lunar-to-Gregorian conversion changes the familiar date. Yi brought roughly 25 mostly panokseon and one turtle ship against 13 proper Japanese warships, described as probably seki-bune with perhaps one or two larger atakebune. He refused to fight beneath troops and arquebusiers on the harbor cliffs, feigned withdrawal, and drew the enemy into open water where Korean maneuverability and cannon could dominate. Panokseon remained at artillery distance while the protected turtle ship closed aggressively; its spiked roof frustrated boarding, and the entire Japanese force was destroyed after several hours, though Yi was wounded by gunfire. The battle joined platform design and tactical choice: the turtle ship accepted the close approach that the artillery ships deliberately avoided.
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Sacheon combines deception, cannon, and the first turtle ship
At Sacheon, Yi lured Japanese warships out of a protected harbor and destroyed them with maneuver, standoff artillery, and a turtle ship that could not be boarded.