The responsibility for the development the Rigid airship having been allotted to the Navy, with this object in view, in the years 1908 and 1909 a design was prepared by Messrs. Vickers Ltd., in conjunction with certain naval officers, for a purely experimental airship which should be as cheap as possible. The ship was to be known as Naval Airship No. 1, and though popularly called the Mayfly, this title was in no way official. In design the following main objects were aimed at: 1. The airship was to be capable of carrying out the duties of an aerial scout. 2. She was to be able to maintain a speed of 40 knots for twenty-four hours, if possible. 3. She was to be so designed that mooring to a mast on the water was to be feasible, to enable her to be independent of her shed except for docking purposes, as in the case with surface vessels. 4. She was to be fitted with wireless telegraphy. 5. Arrangements were to be made for the accommodation of the crew in reasonable comfort. 6. She was to be capable of ascending to a height of not less than 1,500 feet. These conditions rendered it necessary that the airship should be of greater dimensions than any built at the time, together with larger horse-power, etc. These stipulations having been settled by the Admiralty, the Admiralty officials, in conjunction with Messrs. Vickers Ltd., determined the size, shape, and materials for the airship required. The length of the ship was fixed at approximately 500 feet, with a diameter of 48 feet. Various shapes were considered, and the one adopted was that recommended by an American professor named Zahm. In this shape, a great proportion of the longitudinal huff framework is parallel sided with curved bow and stern portions, the radius of these curved portions being, in the case of the bow, twice the diameter of the hull, and in the case of the stern nine times the same diameter. Experiments proved that the resistance of a ship of this shape was only two-fifths of the resistance of a ship of the same dimensions, having the 1 1/2 calibre bow and stern of the Zeppelin airships at that time constructed.