John Wyndham 
The Kraken Wakes 

They came from space, these alien invaders, riding ships like fireballs into the seas and oceans of the Earth. Then they emerged from the depths to wreck havoc on human civilization.

This brilliant science fiction novel, first published in 1953, is another tale of the end of civilization as we know it, from the author of The Day of the Triffids and The Midwich Cuckoos.