The naval Battle of Diu was a sea battle that took place February 3 1509, near Diu, India, between Portugal and a joint fleet of Egypt and the sultan of Gujarat.

The Egyptian fleet, manned mostly by Turks, was sent by the Egyptian sultan to support the Muslim ruler of Gujarat. The Portuguese had a force of 18 ships, commanded by the viceroy Francisco de Almeida. The battle was to avenge the defeat at the battle of Chaul (1508), where the viceroy's son was killed. The allied side had 100 ships, but only 12 were major vessels, the rest were small shallow bottomed craft. The Portuguese ships had guns of greater caliber, better artillery crews, were better manned and better built. The Portuguese naval infantry also had advantage over the Turks, not only because they were heavily armed and equipped (armor, arquebuses and a type of grenade made of clay with gunpowder inside), but also they were seasoned professional seamen, mostly warrior nobility with an huge ascendancy over the Turks, not only in physical strength and size but also in combat skills. With this overwhelming technical superiority, the Portuguese started the battle with a massive bombardment followed by hand-to-hand combat (boarding) in the harbour of Diu, where the allied fleet was anchored. The battle resulted in a decisive victory for Portugal with all Egyptian and Gujarati vessels being sunk or captured without loss and gained uncontested naval supremacy in the Indian Ocean for the next 100 yrs.