Presently he saw the reason for the shadow. It was a huge military Zeppelin, larger than any he had yet seen. Owing to the altitude of the airship it was difficult to judge her dimensions, but by a rough-and-ready comparison with the height of the men who formed her crew, Hamerton came to the conclusion that she was at least eight hundred feet in length, forty-five feet in height and about seventy feet in beam. Not only did she have three cars slung underneath, but on the upper surface of the outer aluminium envelope was a broad gangway, terminating at each end in a wedge-shaped deck-house.
At first Hamerton could see only the rails of the gangway, but as the airship stood farther away to the eastward he discovered four guns so mounted as to be able to fire in a vertical direction, besides being able to be trained abeam.
With the naked eye the Sub counted thirty-two men on board. Others were doubtless in the nacelles, so that he estimated that the crew numbered not far short of fifty.
Unlike the British dirigible, the craft was painted a dull grey on her under body and an olive green above the line of her greatest perimeter. The only splash of bright colour about her was the black cross ensign of Germany that flew from a short staff at the after end of the upper platform.
As the Zeppelin passed over the West Kalbertan Battery her speed was at least thirty miles an hour; but even as the Sub watched she lurched forward and settled down to a pace of nearly thrice her former rate.
In a very few moments she was lost to sight, although flying at an altitude of nearly a thousand feet, travelling in the direction of the North Sea entrance to the Kiel Canal.
"Unwieldy brute!" ejaculated the Sub. "I wonder what headway she would make in a gale of wind? It's a fine day, so I suppose they are taking their pet gasbag for an airing. It strikes me pretty forcibly that they'll have to be pretty sharp about it, for that ground swell is a certain sign of a gale."
Twenty minutes later an air squadron consisting of seven seaplanes flew overhead. The Sub regarded them with curiosity. He had heard that the German authorities, after repeated experiments, had decided to build a number of improved seaplanes to be stationed on the Frisian coast, and now for the first time he saw them in actual flight.
They were flying low—at less than a hundred and fifty feet above the ground; but they flew none the less steadily. The floats were really three boats, the centre one big, about twenty feet in length, and decked in with the exception of two small wells. Immediately in front of the foremost one was a one-pounder automatic gun protected by a V-shaped shield. Abaft the after cockpit was a machine gun of the Maxim type.
On either side of the main float was a subsidiary one, serving simply as outriggers to give lateral stability to the seaplane when resting on the surface of the sea.