The British used blimps for the latter purpose, and to great advantage. The dirigible sausage-balloon, when a submarine is descried, can hover over it (as an aeroplane cannot), remaining as nearly stationary as may be desired, and waiting for an opportunity to drop a bomb with accurate aim.

If the submarine be under water, and its presence betrayed by the peculiar surface-ripple that marks its wake, a bomb with a delay-action fuse can be dropped upon it, the projectile not exploding until it reaches a depth of fifty feet or so. In case the first bomb does not score a hit, there are others to follow, with better luck perhaps.

THE IMPORTANCE OF THE "BLIMP."

Thus, it will be seen that the blimp is an important auxiliary of the flying-machine in the pursuit of the submarines. Both together, in this exciting sport, supplement the swift power-boats called "submarine-chasers."

For some time the Navy Department has trained enlisted men and officers for this work, chiefly at a Gulf port, where a school-it is no war secret-of aviation and ballooning has been maintained. Six officers and 40 men are required for each coast station.

The Navy Department adopted for the blimp a standardized pattern, with definite published specifications, in accordance with which contractors turned them out in numbers. It is a sausage-shaped balloon 160 feet long, with a great diameter of 3112 feet, and containing, when inflated, 77,000 cubic feet of hydrogen gas.

The fabric of the "envelope"-that is to say, of the gasbag-is coated both outside and inside with rubber. It is required that the balloon shall not lose more than 1 per cent of its gas-content in 24 hours. When inflated it must be able to carry (including its own weight) a total of 5275 pounds.

If the "Zeppelin" be excepted, the blimp is the most highly-developed and scientific heavier-than-air flying machine

ever devised. It has a cruising speed of 35 miles an hour, but at a pinch can travel ten miles an hour faster. At the "cruising" rate, it carries enough gasoline to keep going for sixteen hours; at 45 miles, its load of "petrol" will suffice for ten hours.

Even the best war balloons of a few years ago were at the mercy of the winds. It is not so with the blimp. Barring storms, it is able to navigate the air as it wishes. It can rise safely to an altitude of a mile and a half. To furnish fuel for its engine of 100 horsepower it carries, in two tanks, 100 gallons of gasoline.

DESCRIPTION OF THE "BLIMP."

In effect, the blimp is a combination of balloon and aeroplane. Like the latter, it is provided with "skids" (resembling sled runners and made of ash wood), or sometimes with bicycle wheels, for safe landing on terra firma. When designed for sea scouting, floats-cylinders of waterproof fabric stuffed with vegetable fibre-are attached to the skids, or to the wheels, so that the airship, in calm weather, may be able to rest, like a sea bird, on the waves, if desired.

The blimp's balloon envelope must contain two smaller balloons, together holding 19,250 feet of hydrogen gas. The idea, of course, is that if anything happens to the major balloon-puncturing by gunfire or by other mishap the "balloonets" inside of it will keep the machine afloat.

The wingless aeroplane is suspended from the balloon by cables of galvanized wire. There is a special arrangement by which the "pilot"-the man who steers and operates the airship can at any time measure the pressure of hydrogen in the balloon, thus knowing what he has to count on in the way of carrying power.

The front part of the blimp's car is occupied by the engine and radiator, behind which is a bulkhead of sheet steel. In the rear of this bulkhead sits the pilot, and behind him the

"observer," who makes sketches and takes notes of anything important that he sees. Behind the observer are the tanks for fuel oil and 300 gallons of water ballast. The body of the car is covered with aeroplane linen, save for the engine, which is sheathed with sheet aluminum.

In order to hold whatever position in the air may be desired, the blimp is equipped with two horizontal fins and three vertical fins. Not every blimp, that is to say, but the pattern approved and required of contractors by the Navy Department. These fins are made of wood and light steel tubing, reinforced with wire, covered with aeroplane linen rubber painted and finished with varnish.

THE "BLIMP" WELL EQUIPED.

There are also two horizontal rudders and two vertical rudders, for steering up and down or sidewise. They work on ball bearings. A blimp, one should understand, is a fish in the ocean of air, a swimmer-just as the aeroplane is a flyer, like the bird.

The blimp's "car" carries an electric storage battery to furnish lights. The same battery energizes a searchlight for night scouting. A wireless apparatus, for transmitting information to the shore station, is part of the equipment.

The blimp, as already stated, is a sea scout. It is meant to be operated from a base on shore-which base is in constant communication by telegraph and wireless with the great radio stations that are strung all along our coasts at intervals of 200 miles. These stations, in turn, are in communication with the huge wireless outfit at Arlington (across the Potomac from Washington), whose "antennae," uplifted on tall steel towers, receive instantaneous war news from half the world.

Thus if (just for illustration) a blimp spies a hostile submarine, the news is instantly transmitted to the Navy Department. The department orders its "chasers" and warplanes nearest to the scene to go after the undersea boat. Within a

few minutes the pursuit has started, and the U-boat finds itself in much the same situation as a fox hunted by hounds. In this case, however, the hounds are in the air, as well as "quartering" the aqueous terrain.

The United States' blimps are modeled on European patterns. But they are to have special improvements of their own. To make sure of their efficiency and structural correctness, each contractor, in offering bids to furnish them, was required to exhibit a model, exactly like the sausage balloons he proposed to make, but of toy size-one-thirtieth the length of the full-sized, completely equipped aerial sea scout,

CHAPTER IX.

THE EYES OF BATTLE.

AEROPLANES AND AIRSHIPS-THEY SPY THE MOVEMENTS OF FORCES ON LAND OR SEA-LEAD DISASTROUS BOMB ATTACKS-VALUABLE IN "SPOTTING" SUBMARINES THE BOMBARDMENT AT MESSINES RIDGE.

JUS

UST as the submarine has revolutionized warfare on the seas and presented new problems for the naval experts to solve, so the aircraft of the last decade has had its effect upon the operation of land forces. Probably the aeroplane and the dirigible balloon have had a greater influence on the conduct of battles and military campaigns as a whole than any, other device utilized in connection with the war.

It is significant, too, that just as America produced the first submarine, and then failed as a nation to develop it to its highest state of efficiency for military use, so American inventors were pioneers in the construction and successful operation of aeroplanes, or airplanes, which were first developed to their greatest efficiency and utility by the French and Ger

mans.

Some of the most striking events of the war centre around the use of the airplanes or dirigibles, and aside from the picturesqueness and thrilling atmosphere that seem to surround their use, the operator of the aircraft has proved himself one of the most valuable servants in modern warfare. He has reduced the proudest cavalry to second place in the matter of reconnoissance, and has rendered services which have heretofore been impossible.

The air-man sails out over the lines of battle, so far above the earth when necessary as to be out of range of the most powerful guns, and with glasses looks down upon the whole country. His machine, whether it be a dirigible balloon or airplane, is equipped with a wireless telegraph instrument with

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