A submarine torpedo tube bears fairly close resemblance to a large naval gun. Its shape is somewhat similar. It has a barrel with breech and muzzle. As the gun fires a shell, the submerged torpedo tube fires a torpedo, using compressed air rather than an explosive for the purpose. One marked difference between the torpedo tube and a gun, however, is that the torpedo tube's projectile (the torpedo) is self-propelling; the tube supplies only the initial impetus or "start" for the torpedo.

At each end of the torpedo tube, or barrel, is a door-the breech door at the inboard end, the loading or operating end, inside the submarine; the muzzle door at the outboard end, the firing or

ejecting end, opening out into the water. These doors are operated, respectively, by the breech door operating mechanism, and the muzzle door operating mechanism, both of which are located at the breech end of the tube inside the submarine. All

operating mechanism, in fact, is located at and operated from the breech end, the same as with a gun. These mechanisms, which will be described in following pages of this pamphlet, are interrelated and interlocking.

With the muzzle door closed, the breech door is opened, and the torpedo is loaded into the tube. Before opening the breech door, however, the tube must be drained of all water that entered the tube during the preceding firing of a torpedo. For this purpose, there is a system of drains and valves, all operated from the breech end.

The firing mechanism, which sends the torpedo out of the barrel and on its way to the target, includes an impulse tank charged from the submarine's high pressure air system, also a system of valves, gages, etc.

SS204 and 205 have four bow tubes and two stern tubes. All other submarines numbered SS198 or higher have six bow tubes (two vertical rows of

Figure 2 - The submarine torpedo tube's projectile is a torpedo.

Each of the integral parts of the torpedo tube, and their operation, will be illustrated and described, in non-technical language so far as is possible, in the following chapters. Each torpedo is described in a separate pamphlet.

The chapters in this pamphlet should be studied very carefully, so as to become familiar with all parts and their relation one to another, and to the ultimate purpose of the torpedo tube. There should be no hesitancy about asking questions of those in authority. When the time comes for going into action against an enemy, there is no time to wonder or to question about this or that part, or about what should be done first and what next. Operation must be, practically speaking, automatic. Orders must be obeyed instantly. Therefore, assiduous application to the study of this pamphlet is essential.

Figure 3-The breech end of a bow nest of 6 torpedo tubes.

The breech of the barrel is fitted with a door which serves the dual purpose of providing an opening into the tube, and blocking the escape of the compressed air from the barrel by any other means

Figure 5

out the sea while the breech door is opened to allow the torpedo to be loaded into the tube. In this respect, the tube with its interlocked doors acts as an air-lock (like an escape hatch).

A cardinal principle of submarine torpedo tube construction is that one or the other of the tube's two doors must always be closed, to prevent the entrance of the sea into the submarine's interior. As will be shown in following pages of this pamphlet, interlocking devices are fitted to submarine tubes to prevent the simultaneous opening of both breech and muzzle doors. It scarcely seems necessary to

Figure 6

point out the suicidal folly of any attempt to defeat the purpose of these interlocking devices.

With the muzzle door closed to prevent entrance of the sea into the tube, its breech door is opened and a torpedo loaded into it. The breech door is

Figure 7

considerable depth below the sea's surface, there will be water pressure against the muzzle door which may be too great to be overcome by whatever force is applied toward opening it.

To offset this external pressure on the muzzle door, an equal pressure is built up within the tube by admitting water from a tank (simultaneously venting the displaced air into the ship) and then

Figure 8

opening a valve which communicates with the sea. With this done, no more force is required to open the muzzle door than would be needed if the tube and door were not submerged at all.

With the torpedo tube flooded with sea water at the same pressure as that outside the muzzle door, the door is opened and the tube is ready to fire the torpedo. In actual practice, the tube is flooded from

Figure 9

The tube now being ready to fire, a valve between the compressed air supply and the tube is opened. It is obvious that the air pressure must exceed the sea pressure by sufficient margin to force the torpedo out of the tube. Here again, in actual practice, the air charge is not permitted to completely fill the tube and escape into the sea, but is vented off so as to avoid causing a bubble of air to rise to the surface and thereby betraying the submarine's location.

The torpedo having left the tube, the compressed air is shut off, and the tube fills with sea water. This tends to offset the lost weight of the torpedo, keeping the submarine in trim. In effect, this follows actual practice. A submarine is held submerged on level keel at any given depth by taking on or discharging carefully calculated amounts of water ballast. Failure to compensate for the weight of a heavy torpedo can badly upset the vessel's equilibrium.

The torpedo tube having filled with water, the muzzle door is closed, shutting out the sea. It is now possible to open a valve leading to a drain tank, and empty the tube, at the same time blowing in air

Figure 11

to replace the water, and to force it out faster. Thus the weight of the water taken aboard to offset the lost weight of the fired torpedo is retained in approximately the same locality. The breech door may, after all the water is drained out of the tube, be opened for reloading.