CAB38-23 — Page 150

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safety, it is difficult to say what can or cannot be done with regard to accurate navigation, as at present we are chiefly dependent on what can be found out from German data.

5. Ignition of Hydrogen.

As it might possibly be thought that it would not be safe to fire guns from the top of an airship, it might be as well to mention that the ignition of hydrogen in the open air is known to be a matter of considerable difficulty. It is also difficult to get the right proportious of hydrogen and air to form an explosive mixture. In a rigid ship any slight leak of hydrogen would get first into the ring space between gas bag and outer cover, and arrangements are in most Zeppelins made for blowing this space through as the ship travels along. If it were possible to form an explosive mixture anywhere it would only be well behind and above the airship, and quite clear of the airship herself. Very's lights and rifles have been fired with safety from the car of British military airships. There is no fear of guns mounted on the airship igniting the hydrogen if proper precautions are taken.

(For experiment, re ignition of hydrogen by a squib, see paragraph 8.)

6. Use of a Telescope in the "Victoria Luise " (Zeppelin type).

Ordinary binoculars were used by one of our officers in this airship when flying over Bay of Lubeck, along the coast of Kiel, down the Elbe, &c. There is no vibration. The idea that it would be more difficult to use a telescope from an airship than a cruiser is not quite borne out in practice.

7. The German naval lieutenant under instruction in "Victoria Luise " stated that they seldom deflated her- merely topped her up. Allowing the valves to lift freely was the usual practice. If hydrogen is cheap, this is a good way of nearly always flying with a good lift.

8. Aeroplanes as a Defence against Airships, and vulnerability of Airships.

At the present time aeroplanes are of no great value in operating at night.

I am advised that it would not be easy for an aero- plane to close and fly along the top of the airship as close as she likes.

8 (a.) This can be easily tried with the army airships.

For instance, the Zeppelin airship is an almost perfect gun platform, no vibration, little pitching, and provide rifle-proof protection for 8 (b). It is probably as easy to no rolling. She can stop when she likes, rise or the pilot of an aeroplane as to descend. The aeroplane has always to travel at speed. mount Maxims on airships. Dropping a squib on an airship of duo-decagon section would be no easy matter, and the outer cover of the air- ship can be non-inflammable and a squib would not necessarily penetrate it.

On receiving your notes I instructed the Air Department to carry out the following experiments. Two model gas-bags were built to represent the gas- bags in a rigid. In the first experiment, the space between the gas-bag and outer cover was filled with the exhaust gas from a petrol motor. An ordinary service Very's light was fired straight into the gas-bag.

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