"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.