derivation from the French "cascade", which alludes to the tidal surges which flow around them;
derivation from "casque", referring to the helmet-like shape of the rocks;
derivation from "cas" and "quet".
A map dated from around 1640 gives a Latin nameCasus Rupes, which would seem to confirm the third theory above, but which may be a folk etymology.
Wrecks
There have been numerous wrecks on the islets, many of them accounted for by fierce tides reaching 6–7 knots on springs, and a lack of landmarks in the area. The most famous wreck includes SS Stella, wrecked in 1899, with a loss of 105 lives. The largest wreck was the 8000-tonne water tankerConstantia S, lost in 1967. It was believed for centuries that the loss of HMS Victory in 1744 was attributable to wrecking on the Casquets, the lightkeeper of Alderney even being court-martialled for failure to keep the light on at the time of the ship's loss. However, when the wreck of that ship was found in 2008, it was over from the Casquets.
The island was the location of a daring raid by a British commando unit on 2 September 1942. The raid was led by Major Gus March-Phillipps and was one of the first raids by Anders Lassen. In the raid the entire garrison of seven was captured and returned to England as prisoners and the radio and lighthouse wrecked.
In literature
Swinburne's ''Les Casquets''
's poem Les Casquets is based on the Houguez family who actually lived on the island for 18 years. The Houguez were originally from Alderney, and the poem describes their life on Les Casquets. The daughterfalls in love with a carpenter from Alderney but, moving to his island, finds life there too busy. She finds the "small bright streets of serene St Anne" and "the sight of the works of men" too much, and returns to Les Casquets.
Victor Hugo's ''L'Homme qui Rit''
, who lived on Guernsey, and who wrote much about the Channel Islands, says in his novel The Laughing Man, published in 1869:
C. S. Forester's ''Hornblower and the Hotspur''
In this tenth published, but third chronologically, of C. S. Forester's Horatio Hornblower series of novels, the titular hero of Hornblower and the Hotspur is sent to reconnoitre the port of Brest in anticipation of war with France. The Casquets are mentioned as an area that should be negotiated carefully on the way there.