In the meantime another Zeppelin was hovering over the British grand fleet far to the north and was keeping the German Admiral Von Scheer fully informed by wireless of every ship in the squadron. It was this Zeppelin which finally warned the German admiral to return to the protection of secure fortresses and defenses of the great German naval base of Helgoland. By thus saving the Hun fleet from annihilation in this naval encounter it was possible for the Germans to hold a complete, continuous, and dangerous threat that their navy might again come out to attack England or France and cut off English troops from the Continent. This possibility alone compelled the Allies to maintain, until the close of the war, an enormous fleet at all times in the North Sea. There is no gainsaying that in time of war the aeroplane has many advantages over the Zeppelin. The heavier-than-air machine can be produced in quantity much more readily than the lighter-than-air craft. Exact figures on the cost of Zeppelins are not available. W. L. Marsh, in the British publication _Aeronautics_, gives half a million dollars as the estimated cost of a superdirigible of sixty tons, having a lift of thirty-eight tons. This high cost is due, among other things, to the enormous building in which the airship must be constructed, for it must be borne in mind that one of these dinosaurs of the air extends its bulk along the ground farther than the Woolworth Building towers in the air. Indeed, it could not descend in an ordinary city street because of its bulk, and if it did it would extend more than three city blocks of two hundred feet frontage! Moreover, the plant necessary to generate the hydrogen gas sufficient to inflate a bag of two million cubic feet capacity would cost fifty thousand dollars alone. The amount of aluminum in the L-49, forced to land in France in the spring of 1918, would make a foot-bridge over the East River as long as the famous Brooklyn Bridge! To land and house such an elusive and buoyant monster requires many winches and some two hundred men. Even then some have been known to run away. This happened in the winter of 1907, when the _Patrie_, a French semirigid dirigible, which was only a third as large as the German super-Zeppelins, was caught in a gale of wind near Verdun and in spite of the two hundred soldiers who held her in leash she broke her moorings and, flying over France, England, Wales, Ireland, shedding a few fragments on the way, finally disappeared into the sky above the North Atlantic. On the other hand, a six-ton aeroplane can carry a useful load of two tons and does not cost more than $50,000. Also the wing spread of 150 feet of the largest aeroplane is small compared to a 700-foot Zeppelin. Consequently, aeroplanes can be more readily produced in quantity, can be housed, and require only a half-dozen men to take care of them.