The amount of time which a submersible may run beneath the waves depends upon her speed. The best of the German undersea boats, it has been estimated, could not remain under more than three hours at high speed. They then had to come up, as the navy saying has it, for "more juice." To be more explicit, a submersible has a mechanical process, a combination motor and dynamo between the engine, which drives the boat when it is on the surface, and the thrust block through which the shaft runs to the propeller. This motor-dynamo, serving as a motor, drives the boat when she is beneath the water. When the electric power is exhausted the boat comes to the surface, the motor is disconnected from the shaft and is run as a dynamo generating power. Twelve hours are required in which to produce the amount of electricity required for use when the vessel next submerges. Thus, a great proportion of the time the submarine is a surface craft. Again, there are important defects in the lead battery system, which was generally used in the war. First of all, they are very heavy, and secondly the sulphuric acid in the containers is liable to escape--in fact, does escape--when the boat rolls heavily. Sulphuric acid mingling with salt water in the bilges produces a chlorine gas, which, as every one knows, is most deadly. Not only this: the acid eats out the steel plates of a hull. There is talk of using dry batteries, but these are heavy, too, and there are evils arising from their use which have made the lead batteries, objectionable though they may be, preferable in a great majority of cases. The British have a type of submersible propelled on the surface by steam. The Peace Conference at this writing is talking of the advisability of eliminating the submarine as a weapon of war. Whether by the time this is read such action will have been taken, the fact remains that before the submarine could hope to approach in formidability the surface fighter, she will have to experience a development which at the present time has not been attained. The vital need seems to be a single propulsive agency for progress on the surface and when submerged. An interesting table showing the success of the convoy system is herewith presented: