Three Indian Ocean powers built a counter-fleet — Portuguese broadsides sank it in a day

By the early 1500s Portugal had seized the Indian Ocean spice route, and the established sea powers of the region were being squeezed out of a trade they had run for centuries. To reverse it, the Sultanate of Gujarat, the Mamluk Sultanate of Egypt and the Zamorin's Kingdom of Calicut pooled their fleets. At Diu in early 1509 they assembled the largest counter-fleet the Indian Ocean had seen: ten carracks, six heavy galleys, thirty light galleys and up to 150 war boats, carrying thousands of Gujarati sailors and some 450 Mamluk veterans.

The Portuguese admiral Francisco de Almeida met them on 3 February 1509 with a far smaller squadron — nine carracks, six caravels, two galleys and a brigantine, about 800 Portuguese and 400 Nair auxiliaries. The allies had numbers and a purpose-built fleet; the Portuguese had heavier guns served by trained gunners. The engagement was over in a day: every Mamluk ship was sunk or captured, four Gujarati carracks were taken, and the allied force lost roughly 1,300 Gujaratis and 428 Mamluks against just 32 Portuguese dead.

The coalition had adopted gunpowder and built ships for the fight, but built them to fight the way the sea had been fought before — boarding and hand-to-hand. Portugal had moved the decisive weapon to the broadside, a fight the allies' fleet was not organised to win. The battle ended Mamluk naval power in the Indian Ocean and sealed European dominance of the Asian sea lanes for four centuries.