Today, we meet a turtle with an iron shell. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

The Japanese ruler Hideyoshi invaded Korea in 1592. He was armed with a new weapon -- muskets sold to him by the Portuguese. Hideyoshi quickly overran Seoul and seemed to be on his way to conquering the country. Then the Korean government turned to Admiral Sun-Shin Yi. Yi was a brilliant strategist who'd seen war coming and had raised private money to construct a small fleet of utterly remarkable ships called Turtle boats.

The Turtle was ironclad, and it looked like a hundred-foot-long turtle. It had a low, rounded roof, bristling with spikes to prevent boarding. Its sails came down in battle, and it was powered by oars. Just above the oars were ports for cannon, small firearms, and arrows. It had features in common with both Civil War ironclads -- the Monitor and Merrimack -- built 250 years later. The Turtle boats were equipped with rams as well as a dragon's head on the prow. The dragon's head poured out smoke to frighten the enemy and to lay a very effective smoke screen.

During the following months, Yi tore into the Japanese fleet of some 200 ships with his new weapon and devastated it. The war ended in a truce, with Korea divided.

Admiral Yi had stopped the invasion, but he had stirred up political jealousy by doing it. His opponents had him thrown in jail, and there he sat until Hideyoshi renewed the invasion in 1597. With Yi out of the way, the Japanese ravaged the Korean navy. Yi was finally exonerated and put back in charge of just 12 surviving warships.

Less than a month later he ambushed 133 Japanese ships with this tiny fleet. He sank 31 of them and drove the rest off. He also bought time to rebuild his navy.

A year later, the Japanese were fighting a losing war. They began a total withdrawal in an armada of 500 ships. Then Admiral Yi struck them once again with his Turtle -- with this mad, visionary weapon. He sank hundreds of ships -- over half the fleet. The carnage far exceeded the slaughter in Drake's defeat of the Spanish Armada just ten years earlier. In fact, the Japanese loss of 50,000 men was twice the combined number of men who'd merely sailed in the English and Spanish fleets.

The Japanese were so badly beaten that they stayed away from Korea until 1904. Admiral Yi was killed in the battle. And in a strange way, so too was the Turtle. Neither it, nor this huge naval encounter, are even footnotes in Western history books. And we don't see anything like the Turtle again until the Civil War.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

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Jho, S-d., Yi Sung-shin: A National Hero of Korea. Chin Hae: Choongmoo-kong Society, Naval Academy, Korea, 1970.

This episode has been greatly revised as Episode 1540.