A man-of-war is a powerful warship used by navies from the 1500s through the 1800s. These sailing vessels bristled with cannons on multiple decks and carried crews of hundreds of sailors and marines. The largest men-of-war, called ships of the line, might have 100 or more cannons and could devastate enemy fleets in massive sea battles.

The British Royal Navy's men-of-war helped establish Britain as a dominant naval power for centuries. Famous ships like HMS Victory, which fought at the Battle of Trafalgar in 1805, were men-of-war. These vessels didn't just fight: they protected merchant ships, explored unknown waters, and projected a nation's power across the oceans.

When you see paintings of old sailing ships with rows of cannons poking through their sides and multiple tall masts carrying enormous sails, you're probably looking at a man-of-war.

There's also a creature called the Portuguese man-of-war, a jellyfish-like animal with a gas-filled bladder that floats on the ocean surface like a tiny sail. Early sailors thought it resembled their warships floating on the sea, so they gave it the same name.