Man-of-war should not be confused with Portuguese man o' war.
In Royal Navy jargon, a man-of-war (also man-o'-war, or simply man)[1] [2] was a powerful warship or frigate of the 16th to the 19th century, that was frequently used in Europe. Although the term never acquired a specific meaning, it was usually reserved for a sailing ship armed with cannon. The rating system of the Royal Navy classified men-of-war into six "rates", a "first-rate" having the greatest armament, and a "sixth-rate" the least.
The man-of-war was developed in Portugal in the early 15th century from earlier roundships with the addition of a second mast to form the carrack. The 16th century saw the carrack evolve into the galleon and then the ship of the line. The evolution of the term has been given thus:
The man-of-war design developed by Sir John Hawkins was a type of galleon which had three masts, each with three to four sails. The ship could be up to 60 metres long and could have up to 124 guns: four at the bow, eight at the stern, and 56 in each broadside. All these cannons required three gun decks to hold them, one more than any earlier ship. It had a maximum sailing speed of eight or nine knots.