In the history of naval battles, there were limited means of sinking a enemy ship. You could storm it, smash it with some sort of artillery, ram it with one of your own vessels or smuggle George Clooney in as its captain.
"Let's sink this bitch!"
All of these meant getting dangerously close to your target and consequently risking getting sunk yourself. More than 700 years ago, the Muslims saw the folly in this and developed torpedo boats that would be able to sink a ship from a safe distance.
They looked suspiciously like something designed by Cobra Commander.
Sometime between 1270 and 1280, Hasan al-Rammah wrote The Book of Military Horsemanship and Ingenious War Devices. In the book, he describes a torpedo powered by a built-in rocket that could be launched against enemy ships. Using unmanned fire ships had been part of naval strategy for centuries, but they were difficult to aim and required a ship that would have to be sacrificed, sort of like a maritime suicide bomber.
The al-Rammah, as the torpedo was named, was a point-and-fire weapon way cheaper and more efficient than a fire ship. When activated, the torpedo's built-in rockets would propel it through the water, and tail stabilizers would direct it to the target. A spear on the front would impale itself in the hull of an enemy ship, and then the whole damn thing would explode.
Forgotten Until ...
The torpedo, even in a primitive form, wouldn't be invented for another 500 years. If you think about it, it's kind of amazing that boat technology continued to advance by leaps and bounds for centuries, but the technology of strapping a bomb to a piece of metal and making it blow up said boat slowed to a crawl. You'd think the latter would be way easier.
Boats have the advantage of mixing well with musical theater.
And while we're on the subject ...
Around the 14th and 15th centuries, the Chinese had already mastered land mines but were getting increasingly angry at enemy junks floating safely up and down their rivers. So, as described in the aforementioned Fire Dragon Manual, Chinese warlords added sea mines to their arsenals.
Supposedly, this is a picture of one.
Called "submarine dragon-kings," the sea mines were submerged wrought-iron cases packed with explosives enclosed in watertight ox bladders -- basically, a grenade made from the urinary tract of a beast of burden. The explosives would stay dry, but with no oxygen, they couldn't be ignited.
To solve this problem, the ancient Chinese developed an extended fuse that would run from the mine's payload through a snorkel made from goat intestines to a float on the surface disguised with duck feathers, proving that above all else, the ancient Chinese wanted their weapons to be absolutely hilarious.
Case in point: the "flying-cloud thunderclap-eruptor."
Another Chinese war manual describes a later model wherein the timed fuse was replaced by a remote ignition device. By using a cord pulled from the shore, the mine was activated by a flint-and-steel firing mechanism that created a spark in the submerged payload and destroyed any nearby target. Presumably the person hiding on the shore holding the other end of the cord would then blow an air horn and launch into an M.C. Hammer end-zone dance.
Forgotten Until ...
Somehow the technology was forgotten by the West, probably because of that whole Dark Ages thing, and there wasn't another recorded use of sea mines until the Battle of the Kegs in 1778 during the Revolutionary War -- more than 300 years later.
It was totally worth the wait.