Rain ships

Gilbert Norrell used magic to create a fleet of ships out of rain during the Napoleonic Wars. He sent these ships to blockade the French coast, and while the French were confused by the ships and kept to their home ports, the British were able to gain a military advantage, since their own shipping was able to move about quite unhindered[11]. The means of executing this spell are completely unknown.

It was at Brest that the intelligent French Admiral Desmoulins, relying on the customary shrewdness of his servant Perroquet - and with the aid of a certain gallant Captain Jumeau - penetrated the mystery at last. From land, Perroquet had observed that the ships broke all the rules of seamanship. He pointed out to the Admiral that they seemed able to keep their station despite all changes in the wind, etc., and that without resorting to any naval manoeuvres such as tacking or taking in sail. Therefore he, the Admiral and the Captain very bravely took a boat out to observe these baffling ships at close quarters, and quickly realised how they had been deceived. Whether their understanding of the illusion contributed to its ending or no, it was as they looked on with wonder that the spell broke, the ships dissolved into mist, the sea wind blew, and they were gone[11].

White Magic Reveal'd! | Taken from the illustrious Encyclopédie (1772) by Diderot & D'Alembert. The 'vapeur' created by the magician could take the shape of a dove. But that's still a far cry from a complete armada.