In the same year were patented Woodhouse’s submarine, driven by compressed air, and Génoud’s, with a gas-engine worked by hydrogen, which is said to have attained a speed of between four and five knots. Blakesley, in 1884, proposed to use steam raised in a fireless boiler heated by a chemical composition. In 1884, too, Drzewiecki produced the fourth of his ingenious little boats, driven this time not by pedals but by an electric motor. His example was followed by Tuck of San Francisco shortly afterwards, and by Campbell and Ash in their _Nautilus_, which in 1886 underwent very successful trials in the West Indian Docks at Tilbury, near London. In 1886 D’Allest, the celebrated French engineer, designed a submarine fitted with a petrol combustion engine. But the question of propulsion may be said to have been finally settled, within a few months after this, in favour of the electro-motor. For Gustave Zédé’s famous _Gymnote_, which was actually put on the stocks in April 1887, attained in practice a surface speed of 10 knots, and a maximum of 7 to 8 under water. This success saved future designers the trouble of further experiments with ingenious futilities. 5. _Offensive Action._--We have so far been considering the development of the submarine as a vessel navigable under water, without reference to the purpose of offence in war. But this purpose was from the first in view; and with almost all the inventors recorded, it formed the main incentive of their efforts. The evolution of the submarine weapon has been much simpler, and more regular, than that of the vessel which was to use it; but it has been equally wonderful, and the history of it is equally instructive. Briefly, the French, in this department as in the other, have shown the most imaginative enthusiasm, the Americans the greatest determination to achieve results--even with crude or dangerous means--while the English have to their credit both the earliest attempts in actual war, and the final achievement of the automobile torpedo. Of the Germans, as before, we must record that they have contributed nothing of any scientific value.