Torpedo (13th century)
What it is: The first self-propelled projectile for sea warfare.
Why it matters: The Chinese invented gunpowder, but Hassan al-Rammah got the idea of stuffing it into a metal case and shooting it across water to shock and awe an enemy ship. In The Book of Fighting on Horseback and With War Engines (1280), al-Rammah dubbed it a "self-moving and combustible egg." This spiny missile would be filled with saltpeter, flammable liquid, and metal filings. Once ignited, combustion would propel the torpedo to its target, where it might explode.