Despite their name, submarines are really surface boats. Only when necessity demands are they submerged. During the war even the U-boats did 90 per cent of their sailing on the surface. Origially submarines were built primarily for submerged travel and consequently they were given the form of a fish or of a fat cigar, but such a shape was not adapted for surface sailing. Water piled up on the nose of the boat and tended to bear her down. To overcome this, submarines are now shaped more like a boat with a bow high enough to part the waves without burrowing into them. POWER PLANT OF A SUBMARINE The gasoline engines that were formerly used for propelling the boats have now given way to heavy oil or Diesel engines, because of the greater efficiency of these engines and the greater safety of handling heavy oil. Some submarines have been equipped with steam power plants. Such is the power used on the big British submarines above referred to. Of course any power that involves the burning of fuel can only be used on the surface. As has already been explained, an internal combustion engine burns seven to nine times as much air as oil and it would be impossible to store enough air on board to keep the engines going very long; hence they can be operated only while the hatches are open to the atmosphere. Coupled to the shafts of the engines are dynamos which generate electricity and feed it to storage batteries. A dynamo will serve as a generator when turned by some mechanical power and on the other hand when current is fed into it, it serves as a motor, so that when traveling submerged and fuel can no longer be used, the generators are disconnected from the engines but remain connected to the propeller shafts and driven by the very current they previously stored in the batteries. THE COLLAPSIBLE “EYE” OF THE SUBMARINE