But the highly destructive mechanism of water hammer in boiler explosions was understood long before then, as D. K. Clark wrote on 10 February 1860, in a letter to the editors of "Mechanics Magazine":"The sudden dispersion and projection of the water in the boiler against the bounding surfaces of the boiler is the great cause of the violence of the results: the dispersion, being caused by the momentary generation of steam throughout the mass of the water, and in its efforts to escape, it carries the water before it, and the combined momentum of the steam and the water carries them like shot through and amongst the bounding surfaces, and deforms or shatters them in a manner not to be accounted for by simple overpressure or by simple momentum of steam."Boiler explosions are common in sinking ships once the superheated boiler touches cold sea water, as the sudden cooling of the superheated metal causes it to crack; for instance, when the was torpedoed by a U-boat, the torpedoes and resulting boiler explosion caused the ship to go down in two minutes, leaving Poon Lim as the only survivor in a complement of 54 crew.