A torpedo tube is a device for launching torpedoes in a horizontal direction.
There are two main types of torpedo tube:
Those designed to operate below water level, as fitted to submarines and some surface ships
Deck-mounted torpedo launchers on surface ships only
Some authorities prefer to reserve the term torpedo tube for submarine type torpedo tubes, referring to deck-mounted units as torpedo launchers, but the more general use has long been widespread among both lay people and arms manufacturers.
There are essential differences between the two types other than the obvious one of operating in air as opposed to water. Deck-mounted launchers are normally designed for a specific munition, and often for a particular model of that munition. On the other hand, the torpedo tube is the submarine's general purpose launcher, and the only one capable of being reloaded while submerged. In contrast, missile tubes and the newer vertical launchers are each loaded with a single round while in port.
The more recent designs of submarine torpedo tube may even be used for more than one size of torpedo, as well as other munitions including mines and cruise missiles. Submarine tubes of greater than 21 inches in diameter are designed to accept the standard 21 inch heavy torpedo as well as larger munitions.
Some nuclear submarines, both US and Soviet, were fitted with two sizes of torpedo tube. On these boats a set of smaller tubes were dedicated to firing torpedoes, while the larger tubes were intended to fire a wide variety of munitions. This provided versatility and firepower while saving space, cost and complexity over an armament of all larger tubes.
On the older Soviet boats such as the Hotel class submarine, the smaller tubes were 16 inch, with the general purpose tubes being the standard 21 inch. On others, such as the Soviet Akula class submarine, the smaller tubes were 21 inch. More recently both navies appear to be returning to a smaller number of only 21 inch tubes.
See torpedo for a list of torpedo sizes.
Submarine torpedo tube
A submarine torpedo tube is a more complex mechanism than a torpedo tube on a surface ship, because the tube has to accomplish the function of moving the torpedo from the normal atmospheric pressure within the submarine into the sea at the ambient pressure of the water around the submarine. Thus a submarine torpedo tube operates on the principle of an airlock.
Torpedo tube operation
The accompanying diagram illustrates the operation of a submarine torpedo tube. The diagram is somewhat simplified but shows the workings of a submarine torpedo launch.
A torpedo tube has a considerable number of interlocks for safety reasons. For example, an interlock prevents the breech door and muzzle door from opening at the same time. Also, the breech door cannot be opened when the tube is filled with water.
The following steps explain, in simplified form, the submarine torpedo launch sequence.
Open the breech door in the torpedo room. Insert the torpedo into the tube.
Hook up the wire-guide connection and the torpedo power cable.
Shut and lock the breech door.
Turn on power to the torpedo. A minimum amount of time is required for torpedo warmup.
Open the vent valve.
Open the 3-way flood/drain valve to the flood position. Pressure in the flood tank forces water into the torpedo tube, while the air in the tube is forced out the vent valve. When the flood sensor in the vent tube senses water in the pipe, the tube is filled and the flood/drain valve shuts.
Shut the vent valve.
Open the equalizing valve to equalize pressure in the tube with ambient sea pressure.
Open the muzzle door.
Open the slide valve, which provides the path for water from the water ram to the tube.
When the launch command is given and all interlocks are satisfied, the water ram operates, thrusting a large volume of water into the tube at high pressure, which ejects the torpedo from the tube with considerable force. In fact, modern torpedoes have a safety mechanism that prevents activation of the torpedo unless the torpedo senses the required amount of G-force.
When the torpedo receives the launch command, it severs its power connection to the tube and begins operating on its internal battery. This “crossover battery” provides power for a few seconds to operate the electronics and start the motor once the torpedo is out of the tube.
Once outside the tube, the torpedo motor starts and the torpedo begins its run toward the target.
For wire-guided torpedoes, the muzzle door must remain open because the guidance wire is still connected to the inside of the breech door to receive commands from the submarine’s fire-control system. The wire cutter on the inside of the breech door can be activated at any time.
Shut the slide valve.
Shut the muzzle door.
Shut the equalizing valve.
Open the 3-way flood-drain valve to the drain position.
Open the blow valve, which pressurizes the torpedo tube and forces the water in the tube down into the drain tank. This is called “blowing down” the tube.
When the tube is dry, shut the blow valve and shut the flood/drain valve.
Open the vent valve and vent the tube to ambient atmospheric pressure.
Open the breech door and remove the remnants of the torpedo power cable and the guidance wire.
Shut and lock the breech door.
End of sequence. The tube is now ready for another launch.
Water drained from the tube after a launch remains in the drain tank to compensate for the weight of the torpedo that was launched. When the drain tank becomes full, the water can be pumped from drain tank back into the flood tank.
Submarines Launching Torpedoes
The method of launching torpedoes varies. Modern submarines have fixed tubes in the bow area from which torpedoes can be ejected by compressed air, either while the submarine is submerged or while it is surfaced. Surface vessels have tubes similar to those of submarines except that they can be aimed independently of the boat's orientation; a charge of gunpowder is used to eject the torpedo. Aircraft drop torpedoes from special bays while flying at low altitudes. PT boats, now obsolete, launched torpedoes from launching racks that slid the torpedoes into the water.
Torpedoes often zero in on a target by electronically monitoring underwater sounds. Some torpedoes move toward the sounds the target ship or submarine makes; other torpedoes emit sound pulses, then move toward the sound reflections that bounce off the target vessel. Torpedoes detonate upon striking the target vessel's hull or use a magnetic sensor to trigger the explosion near the vessel's hull. The force of the explosion either sinks the ship or submarine outright, or so weakens the superstructure that it may break apart by normal sea turbulence.