Deeds of a Great Railway / A record of the enterprise and achievements of the London and North-Western Railway company during the Great War

by G. R. S. Darroch

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.

"Two paravanes," as Mr. McKay explains, "are towed, one on either side of the vessel, ... and the action of the protector-gear is simple. The paravane towing-wires foul the mooring-wire of any mine which might strike the vessel, but misses any mine which is too deeply anchored. The speed of the vessel causes the mine and its sinker to be deflected down the 'wedge' and away from the vessel until the mine mooring-wire reaches the paravane," which wire "passing into the cutter-jaws is speedily severed; the sinker drops to the bottom of the sea, whilst the mine floats to the surface well clear of the ship, where it can be seen and destroyed by rifle fire."

The jerky sawing action of the mine mooring-cable, on reaching the jaws of the paravane, was, perforce, extremely detrimental to the teeth of the cutter-blades; consequently it was invariably the practice to haul the paravane aboard the ship and examine the blades immediately after a mine had been trapped and destroyed. The peril of pottering about, unprotected, in a mine-field must be patent to all, particularly to those who happen to be doing the pottering; hence it was absolutely essential that brackets and blades should be so accurately machined and fitted that the latter, on being removed, could be replaced in an instant by "spares" and the paravane dropped straight back into the sea.

Speaking in the House of Commons (cp. the Times, March 21st, 1918), Sir Eric Geddes, then First Lord of the Admiralty, said that for the twelve months of unrestricted warfare from February 1st, 1917, to January 31st, 1918, the actual figures of vessels sunk by submarine action, including those damaged and ultimately abandoned, amounted to roughly six million tons; that the (then) total world's shipping tonnage (exclusive of enemy ships) was forty-two millions; and that the percentage of net loss to British tonnage was 20 per cent.

Mr. McKay, too, in his article previously quoted, gives some interesting figures which tend to recall the gloomy days of rationing cards, and help us to realise how deeply we are indebted to Commander Burney and his paravanes for assuring us to the bitter end our daily, if slightly curtailed, means of subsistence. "It is computed," writes Mr. McKay, "that the total loss in shipping due to submarine warfare is about £1,000,000,000. Hence, working on the certainties, each submarine destroyed was responsible for about £5,000,000 worth of damage. Accepting this figure as a basis, it may be said that the explosive paravanes saved further damage being inflicted on our shipping to the extent of about £25,000,000." Reverting next to the protector paravane, "there were," we are told, "about 180 British warships fitted with the installation. Assuming that the value of warship tonnage is placed at the very low average figure of £100 per ton, the value of the ships saved was above £50,000,000;" and a further point which cannot be ignored is that undoubtedly "the moral effect of the loss of these vessels would have been stupendous."