Hermes was already an antique by 1913. Built at Fairfield's Govan yard, launched in 1898 by Lady Kelvin, she had served as flagship on the West Indies, East Indies, and Cape of Good Hope stations - the kind of imperial cruising the Edwardian navy liked. She had eleven six-inch guns, eighteen finicky Belleville boilers eventually swapped out at Belfast, and a top speed of 20 knots from 10,000 horsepower. By the time she came home to the Nore Reserve in March 1913, she was a relic. Then somebody in the Admiralty looked at the bare forecastle, at the open quarterdeck, and decided she would do.

In April 1913, workmen at Portsmouth pulled out the forward six-inch gun and laid a tracked launching platform over the bow. A canvas hangar went up aft of the rails. A derrick was rigged from the foremast to lift seaplanes back out of the water. Two thousand imperial gallons of petrol went into tins in lockers below. By 7 May she was recommissioned as the Royal Navy's first experimental seaplane carrier, with room for three machines: a Borel Bo.11 monoplane, a Short Folder with its hinged wings, and later a Caudron G.2 amphibian after a storm wrecked the Borel. On 28 July a Caudron lifted off her deck while she was under way - one of the earliest successful launches from a moving British warship.

In the 1913 fleet manoeuvres, Vice-Admiral John Jellicoe's Red Fleet needed a Zeppelin to scout against, and Hermes was told to pretend. The Short Folder, weighted to its limit, could only carry a tiny wireless transmitter, so it would fly off, spot ships, and signal back to Hermes - which would relay the report on her bigger wireless. About thirty flights went up before 6 October. The conclusions, written down in clipped Admiralty prose, are obvious now and were not obvious then: aircraft needed proper radios to be useful as scouts, sustained naval flying was possible at sea, and converted landplanes were not the answer. Every aircraft carrier that ever launched a strike traces back to those weeks. Hermes was paid off again in December, the experiment over.

When the war began in August 1914 she was hurriedly recommissioned, this time as an aircraft ferry and depot ship for the Royal Naval Air Service. On 30 October she crossed to Dunkirk with a deck-load of seaplanes for the squadrons defending the Channel ports. The next morning she put back to sea for home. Somewhere out in the Straits of Dover a wireless signal warned her of a submarine in the area, and her captain ordered her recalled. She was zigzagging at 13 knots when U-27, commanded by Bernd Wegener, fired from 300 yards. The torpedo found her amidships. She rolled and went down off Ruylingen Bank in shallow water with the loss of 21 of her crew.

She is a war grave now, protected under the Protection of Military Remains Act 1986. In January 2017 two English divers were charged with failing to declare items they had brought up from her hull - a reminder that she is still down there in roughly thirty metres of water, upside down, the canvas hangar long gone but the hull intact enough for trespassers to fancy a souvenir. Her name passed on: the next HMS Hermes was a real aircraft carrier, and the one after that fought in the Falklands. The lineage starts here, in the strait, with an old cruiser and a wooden flight deck and a torpedo on a clear cold morning.