If in only a minor degree--for those who go down to the sea in ships are necessarily many in number, and the business which they do in great waters is of an extremely varied nature--Crewe was nevertheless called upon to put this theory into practice in the land and sea war that burst upon us in 1914; and one of the mechanical contrivances which was destined to play an inordinately important part in securing this "perfect co-ordination and co-operation" as between the land and sea forces of the country, and for various essential component parts of which Crewe became responsible, was the "Paravane;" and the paravane, being by nature something entirely novel, was _ipso facto_ one of those devices which had to fight the War Office, or the Admiralty, as the case might be, before it got a chance of fighting the enemy. Primarily devised for the purpose of subverting the submarine peril, the paravane (the invention of Acting-Commander Burney) was later adapted for the protection of vessels against mines. An extremely interesting and lucid account of this mechanical contrivance, from the pen of Mr. R. F. McKay, is to be found in _Engineering_, under date of September 19th, 1919. [Illustration: THE PROTECTOR, OR MINE-SWEEPING, PARAVANE. [_To face p. 70._] Mr. McKay tells us that there were various types of paravanes, known respectively as the explosive, the protector, and the mine-sweeping paravane. Briefly, the device was a torpedo-shaped body, which, towed by a suitable cable either from the bows or stern of a ship, maintained its equilibrium in the water by means of a large steel plane near its head, and horizontal and vertical fins near its tail, the thrust of the water on the plane when the vessel is in motion carrying the paravane away from the fore and aft centre line of the vessel. Depth mechanism was fitted in the tail of the paravane, and consisted of a horizontal rudder actuated by a hydrostatic valve, _i.e._ a valve which is operated by difference in water pressure due to any change in depth. The explosive paravane was towed from the stern, and the charge of T.N.T. which it contained could be detonated either by impact, or by an excessive load coming on to the cable, or by a current of electricity controlled from the ship. The protector or mine-sweeping paravanes were similar contrivances in that they were towed, and maintained their position in the water by similar means. They were, however, towed from the bows of the ship, and instead of carrying an explosive charge, they were fitted with a bracket resembling a pair of jaws, in which were fixed two saw-edged steel blades; and it was in the manufacture of these brackets, which were forged under the drop-hammer, that Crewe was engaged.