"Patrol duty is a grind. The sea where we work is filled with wreckage for a distance of 300 miles off shore, and you can take almost any floating object for a periscope. Yes, we shoot at everything; ours is not a business in which to take chances. Convoy work is more interesting and more exciting than the round of patrol. The advantage of the convoy over the picking up and escorting of a merchantman by a patrol-boat is that in the convoy from six to ten destroyers can protect from ten to thirty merchantmen, while under the patrol system one destroyer watches one merchant craft. Convoy trips take our destroyers away from their base from six to eight days, and they are all trying days, especially so in dirty weather. On convoy duty no officer, and no man, has his clothes off from start to finish. Too many things may happen to warrant any sort of unpreparedness. Constant readiness is the watch-word. "At night difficulty and danger increase, chiefly because of the increased danger of collision. Collisions sometimes occur--what with the absence of lights, the zigzag course of the ships of the convoy, and the speed with which we travel. But as a rule the accidents are of the scraping variety, and all thus is usually well. The convoy is purely a defensive measure. The patrol is the offensive; in this the destroyers and other craft go out and look for the U-boats, the idea being to hound them out of the seas." Then there are netting operations in which our sailors have played some part. The netting most often used is made of stout galvanized wire with a 15-foot mesh. This is cut into lengths of 170 feet, with a depth of 45 feet. On top of this great net are lashed immense blocks of wood for buoys. Two oil-burning destroyers take the netting, and hanging it between them as deep down in the water as it will go, are ready to seine the 'silverfish.' The range of a submarine's periscope is little over a mile in any sort of sea. Vessels that are belching clouds of smoke may be picked up at distances of from three to five miles, but no more. In other words, watchful eyes gazing through binoculars may see a periscope as far as that periscope sees. The destroyers, bearing their net between them, then pick up a distant periscope. They chart the submarine's direction (this may be told by the direction in which the periscope is cutting the water) and calculate her speed. Then they steam to a point directly ahead of the submarine, and the lashings are cut away from the net. While it thus floats in the submarine's path the destroyers speed away out of eye-shot. In a large majority of cases it is claimed the submarine runs into that net, or one like it. Results are a probable disarrangement of her machinery and her balance upset. She may be thrown over on her back. If she comes up she goes down again for good and all with a hole shot in her hull; if not, it is just as well, a shell has been saved.