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 engine down to about two pounds per horse-power and the weight of the fuel required to about half a pound per horse-power hour. Even with these reduced weights the burden that has to be supported by an aeroplane starting on a long flight or on a bombing expedition is most formidable though it may be completely satisfactory for the aeroplanes which have to discharge their ordinary functions at the front. The weight of a fully equipped aeroplane varies from half a ton to several tons and its speed may go up to 100 miles or even 120 miles per hour. No one could suggest that any form of motor would be capable of discharging such duties other than the internal combustion engine.

In the same sense that the internal combustion engine made the aeroplane a practical proposition it must be said to have given us the Tanks. The essence of their success was their shape, the efficiency due to their compactness, and the perfect drive which they got from the endless tracks which ran round their periphery on each side. Many would 32