The carrying of large quantities of petrol, or heavy oil, is under all circumstances attended with a certain amount of risk, and when many tons have to be carried in a confined space, as in a submarine, this risk is more than doubled, as the slightest leakage when the vessel is submerged would mean that a powerful explosive mixture of petrol and air would be made.
A modern submarine torpedo-boat (British type). A. Deck superstructure. B. Scuppers for filling superstructure. D. External connections. E. Conning-tower (4-inch armour). F. Periscope. G. Periscope motor (for turning, &c.). H. Air cowls. I. Conning-tower cap (opening sideways). J. Mast stays. K. Mast (not part of service equipment). L. Torpedo-tube cap. M. Torpedo-tubes (twin), torpedoes in. N. Air-flask (for expelling torpedoes). O. Hydroplane engines. X. Double casing, with special vent for accumulators. Y. Spare torpedoes. Z. Petrol storage tanks (2). 1. Air flasks. 2. Centrifugal pumps. 3. Air-lock, with submarine escape dresses. 4. Commander’s platform. 5. Ladders. 6. Depth and deflection indicator, registering submarine’s deflection from horizontal. 7. Speed dials. 9. Petrol engines. 10. Electric engines. 11. Dynamo, for recharging batteries. 12. Petrol engines—exhaust.
It being also quite impossible, for obvious reasons, to use a petrol engine when running submerged, a second motive power, an engine, with its additional space and weight, has to be carried to drive the submarine when under water. For this purpose electricity is used in almost all types. But electricity, again, has many drawbacks. It costs in weight nearly thirty times more than other motive powers, and is extremely dangerous, for should salt water in any way gain access to the storage batteries, chlorine gas would be given off in large quantities, although in the more recent vessels of the British, American, and French Navies this danger has been minimised by enclosing the batteries in air-tight cases. On account of the weight and the space required, it is impossible to install a very powerful electric engine in a submarine (compared with the size of the boat), and thus both the speed and radius of action are curtailed.
If this division of power between the surface and submerged engines could be overcome, and the whole space made available for one powerful set of engines suitable for driving the vessel both on the surface and when submerged, not only would the mechanism of submarines be simplified, but a very considerable increase in both speed and range of action would naturally result.
In the “D,” “E” and “F” classes of British submarines, and in the more modern vessels of the French, Russian and German Navies, heavy oil is being used in place of petrol on account of the increase in power obtained with greater safety.
Arrangements are made in almost all modern submarines so that when the vessel is using the oil engines for running on the surface the electricity for use when submerged is being made by a dynamo and stored in batteries. From this it will be seen that there are really three separate engines in a submarine:—(1) the oil or petrol motor, which drives the vessel when on the surface, and, at the same time, by a suitable arrangement of gearing, operates a dynamo, (2) which makes the electric current for storage, and (3) an electric engine which drives the vessel when submerged, obtaining the necessary power from the batteries.
It is, however, technically incorrect to say that there are two sources of power in a submarine, for electricity is not, in itself, a source of power, but merely a handy method of storing and transmitting it. The only actual source being the oil or petrol.
There are also numerous small engines to add to the complexity of machinery in a submarine, such as the air compressors used for charging the torpedo tubes with compressed air for expelling the torpedoes and for other purposes, and electric motors for operating the pumps, steering mechanism, and periscopes. In addition to all this, hand-mechanism is provided for use in case of a breakdown to operate most of these important appliances. Then again there is, of course, the armament mechanism for working the torpedo tubes and semi-automatic quick-firing guns.
From the foregoing it may appear that the interior of a submarine presents a picture of mechanical complexity utterly incomprehensible. Yet such is not the case. The fanciful belief that the crew stand, boxed up in these vessels, sweating with the heat, struggling for breath, and with crank-shafts whirling uncomfortably close to the small of their backs, electric motors buzzing within a few inches of their ears, and nervous hands grasping one or other of the levers ranged in rows in front of them, is, doubtless, most romantic, but quite unreal. Much of the undoubtedly complicated machinery in a submarine is tucked away in the conical extremities, under the interior decking, and fixed to the arched steel sides. The centre is left almost entirely clear, so that trestle-tables may be erected for meals, hammocks swung for sleeping, and sufficient space allowed to make these small vessels as habitable as possible. Not the least difficulty of the submarine designer is to create order and leave space among the chaos of machinery which has to be installed in these peculiar and deadly little torpedo craft.