A torpedo tube is a device for launching torpedoes in a horizontal direction.
There are two main types of torpedo tube:
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. In contrast, missile tubes and the newer vertical launchers are each loaded with a single round while in port. However, it is unclear why information about VLS for missiles pertains to torpedo tubes, unless it is supposed to be an attempt at comparison of relative value in combat. A torpedo tube can be reloaded at sea, while a missile system can't. Fortunately the military has spent a great deal of time and money developing and comparing the two, and ultimately relies on both.
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.
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.
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.
Spare torpedoes are stored behind the tube in racks. Various types of handling systems exist for loading torpedoes into the tubes but they are essentially hydraulic or manual. Prior to the Ohio class, U.S. SSBN's utilized a manual system of ropes, pulleys and such. About 15 minutes would be needed to reload a tube in this way. SSN's prior to the Seawolf class used a hydraulic system that was much faster and safer in conditions where the ship needed to maneuver. It is important to remember that when handling ordnance, safety is more important than speed.
The German Type 212 submarine uses a new development of the water ram expulsion system, which ejects the torpedo with water pressure to avoid acoustic detection.