Why is the man-of-war called man-of war?

Answer 1

No one knows for sure. But there are at least two conflicting theories.

The most popular is that it was named after a medieval Portuguese sailing vessel, called a caravel, since the marine colonial hydrozoan also plies the open oceans using its pneumatophore (float) as a sail. However, since the term 'Man of War' specifically refers to a later British design, you would have to assume that the seventeenth century term for an English fighting ship was applied to the fifteenth century Portuguese scouting and trading vessel. And, you would also be hard pressed to see any similarity between the creature's rounded sail and either a lateen-rigged (triangular shaped) caravel sail, or a square-rigged carrack sail.

What seems much more plausible to me is that it is named after the helmet worn by Portuguese soldiers (men of war). That helmet is called a comb morion. If you Google an image of the helmet, you will see a striking similarity in appearance. Just saying, but then I also think fluorescent road cones look like psychedelic witches emerging from the center of the earth.

Answer 2

The shape is similar to the military sailing ship known as a man-o-war.

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A Man of War ship was generally a term used for an English ship of the line, with neither the shape nor the sail resembling the round shape of a man-of-war float. Portugal did not have a ship resembling that unique shape, either. However, some say that the English were ridiculing the smaller Portuguese caravel ship by calling the floating jelly a disparaging term for the ships of the waning Portuguese navy.

Or, it may look like a Portuguese man of war helmet, a comb Morion. The shape of a physalia's float looks remarkably like a 16th century Portuguese soldier's helmet. Since no firm references have been found for the origin of the term, anyone's opinion is as valid as the next.