ached; petrol tanks were placed inside the envelope, under which
was rigged a long covered-in car, built up of a light steel tubular
framework 35 feet in length. The forward portion was covered with
duralumin sheeting, an aluminium alloy which, unlike aluminium itself,
is not affected by the action of sea air and water, and the remainder
with fabric laced to the framework. Windows and port-holes were provided
to give light to the crew, and the controls and navigating instruments
were placed forward, with the sleeping accommodation aft. The engines
were mounted in a power unit structure, separate from the car and
connected by wooden gang ways supported by wire cables. A complete
electrical installation of two dynamos and batteries for lights,
signalling lamps, wireless, telephones, etc., was carried, and the
motive power consisted of either two 250 horse-power Rolls-Royce engines
or two 240 horse-power Fiat engines. The principal dimensions of this
type are length 262 feet, horizontal diameter 56 feet 9 inches, vertical
diameter 69 feet 3 inches. The gross lift is 24,300 lbs. and the
disposable lift without crew, petrol, oil, and ballast 8,500 lbs. The
normal crew carried for patrol work was ten officers and men. This type
holds the record of 101 hours continuous flight on patrol duty.

In the matter of rigid design it was not until 1913 that the British
Admiralty got over the fact that the 'Mayfly' would not, and decided on
a further attempt at the construction of a rigid dirigible. The
contract for this was signed in March of 1914; work was suspended in the
following February and begun again in July, 1915, but it was not until
January of 1917 that the ship was finished, while her trials were not
completed until March of 1917, when she was taken over by the Admiralty.
The details of the construction and trial of this vessel, known as 'No.
9,' go to show that she did not quite fill the contract requirements in
respect of disposable lift until a number of alterations had been made.
The contract specified that a speed of at least 45 miles per hour was to
be attained at full engine power, while a minimum disposable lift of 5
tons was to be available for movable weights, and the airship was to
be capable of rising to a height of 2,000 feet. Driven by four Wolseley
Maybach engines of 180 horse-power each, the lift of the vessel was not
sufficient, so it was decided to remove the two engines in the after
car and replace them by