Attention has since been concentrated in most part on the construction of aeroplanes in constantly increasing numbers, although the dirigible has not been given up altogether. However, its restricted usefulness as well as the necessary limitations of its effective size has been recognized. Early in the war Great Britain planned the construction of fifty small dirigibles, of both the rigid and nonrigid types, all of which have undoubtedly since been completed. They are small airships designed chiefly for scouting and short-range bombing raids over camps when in army service and for coast patrol and submarine hunting as an aid to the naval forces. While no specifications are available, the cubic capacity of these patrol airships probably does not exceed 50,000 to 75,000 cubic feet, their over-all length being approximately 100 to 125 feet. [Illustration: Fig. 20. An Early Type of Small British Dirigible] *Aeroplane Features.* To simplify the construction and at the same time minimize the amount of head resistance, the car consists of an aeroplane fuselage of the tractor type, fitted with a comparatively small motor—under 100 horsepower—and having accommodations for a pilot and an observer in two cockpits, placed tandem. The control surfaces are also similar to those used in aeroplane construction. Despite their low power, these dirigibles can make 40 miles an hour, owing to their greatly reduced head resistance. Instead of employing either an auxiliary blowing motor or a blower driven by the motor itself, the supply duct to the air balloonet is made rigid and is sloped forward so that its open end comes directly in the slip stream of the propeller; thus the latter serves to inflate the balloonet as well as to drive the dirigible. The desired amount of inflation is controlled by a valve. [Illustration: Fig. 21. Side and End Views of British Astra-Torres Dirigible Used for Anti-Submarine Patrol Service] *Use in Locating Submarines.* Many of these small scouting and naval-patrol dirigibles have given a good account of themselves and comparatively few have met with accident or have been destroyed by the enemy. On frequent occasions they have been very successful in locating submarines below the surface, since the body of the under-water boat is readily detected from an altitude of a thousand feet or more, even though submerged to a great depth and despite a heavy ripple on the surface that makes the water absolutely opaque when viewed from the deck of a ship. Doubtless they will be employed to an increasing extent as the hunt for the submarine becomes more and more intensive, though their use is very much restricted during the winter months, owing to the frequent and severe storms encountered.