She was a hundred and eleven feet long, and was the sole survivor, but one, of fifteen similar boats. She carried twelve mines in four vertical tubes forward of her conning-tower.
Her Commander passed the North Hinder and pushed on towards England, running on the surface across our deep mine-field. When in sight of the shipping channel he dived and worked his way right into the approaches to Harwich. He was a bit early, for it was still daylight, and he liked to lay his mines at high water, as this gave him a greater depth for diving.
He loafed along at two knots, thirty feet under the surface, with his periscope twelve inches above water, keeping a sharp look-out for trouble. Presently he saw a fleet of mine-sweepers working in the distance, and creeping cautiously closer, observed that they were sweeping in an area between four bright-green buoys, marking off the corners of a large parallelogram. Consulting the chart supplied by his intelligence department, he saw that the trawlers were sweeping in the emergency war channel.
The mine-sweepers were working in pairs, travelling abreast and some distance apart. Each trawler towed a kite at the end of a wire cable. The heavy wooden kite was V-shaped and sank under the surface to the required depth when towed. Between the two kites was a wire rope. It had chains attached to it, so that it dragged on the bottom, and rollers, so that it would not foul. In the bight of the wire was a serrated portion. The idea was to catch the mooring cable of any mine on the wire and saw it in two on the serrations. The mine would then rise to the surface and could be destroyed by rifle fire.
The Commander of U-C 1 told his second in command that these preparations clearly meant that the Harwich Light Forces were going to take a burst out to sea, and that he intended to lay a line of mines across their path.
At dusk the trawlers packed up and boiled off for home at top speed. The German Commander watching them said: "It is easy to see that they are burning Government coal."
Just before high tide the U-C 1 entered the parallelogram inside the four green buoys, still under water. She was a third of the way across when a sharp order was given, a lever was pulled, and a mine left one of the tubes.
The complete mine consisted of two parts, the war-head and the sinker.
As it left the submarine it slowly sank to the bottom and rested on its sinker, for in the war-head was an air chamber which kept it right end up.
A slow spring, automatically released when the mine left the tube, began to move a lever, and at the end of five minutes it pulled back a catch and released the war-head from the sinker.