The mine-laying submarines of the Harwich Flotilla were especially busy on the eastern side of the North Sea, where our great minefields were. Captains of submarines describe this portion of the sea as an ideal one for submarine work; for the depth of the water is generally of from twenty to thirty fathoms, at which depth a submarine can lie comfortably at the bottom without being subjected to an excessive pressure. Comfortable is, of course, a relative term. Most people would never be anything but extremely uncomfortable in the atmosphere of a submarine after she has been submerged for some hours. A fresh-air crank would die in it. The great minefield which was declared by our Government in the summer of 1917, the preparation of which was a gigantic undertaking, extended from the Frisian Islands to about latitude 56 degrees north. The Dutch, for their own purposes, removed their lightships from their coasts to the western side of this minefield, thus forming a line of lights running north and south, roughly along the 4th degree of east longitude. This our sailors facetiously named Piccadilly Circus. It was the business of the submarines to lay mines on the eastern part of this minefield, that is, near to the coast. Our surface mine-layers laid their mines further seaward; while still further west our large mine-laying ships, one of which can carry as many as three hundred mines, laid their mines just inside Piccadilly Circus. Our submarines used to patrol regularly along Piccadilly Circus to look out for and attack enemy ships, and at intervals went shorewards through the minefield in order to reconnoitre. A mine-laying submarine used to adopt the following methods. She would get close under the enemy coast under cover of the night and then dive, to remain at the bottom until the morning. As soon as there was light enough she would rise until her periscope was above the surface, and ascertain her position by cross bearings of the shore taken through her periscope. Then she would move to the different positions at which she had to lay her mines, all the while using her periscope for the taking of cross bearings. When she had completed her work she would return home by night, travelling on the surface as before. The patrolling submarines were bombed constantly by enemy Zeppelins and seaplanes, but with little effect. To the submarine the mine was by far the greatest danger, and no doubt the depth charge too accounted for some of our casualties. But, as I have said, in nearly all cases when a submarine is lost, no one knows what has happened. She merely does not come back. The mine-laying of the Harwich submarines was chiefly directed against the enemy submarines, the mines being generally laid at about eight feet below the surface, so as to catch these craft while travelling on the surface. They were also laid at forty feet or more, so as to strike the submarines when travelling under water.