# Flooding submarine torpedo tubes from the inside **URL:** \ **Category:** Factual Questions\ **Created:** [October 13, 2014, 11:23pm UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250 "2014-10-13T23:23:22Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [October 13, 2014, 11:23pm UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/1 "2014-10-13T23:23:22Z")
As I understand it, flooding submarine torpedo tubes from the outside by opening the tube doors creates noise (and betrays one’s location to the enemy) because of the ocean water rushing into the tube and the bubbles storming out to the surface. Why couldn’t submarine torpedo tubes be filled from the inside with water leading from plumbing from the submarine’s own internal water supply? …And _then_, once the tubes were filled, you could open the tube doors? It would be much quieter, would it not? ---
**Author:** ![Kobal2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kobal2/32/20_2.png) [@Kobal2](https://boards.straightdope.com/u/Kobal2)\ **Post date:** [October 13, 2014, 11:59pm UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/2 "2014-10-13T23:59:05Z")
The tubes are filled with water \*before \*opening the doors. To equalize pressure - else they’d be really hard to open and make even more noise. High pressure water rushing in might even damage the torpedo, I 'unno. As for how or whence to fill them : anyway you slice it you’ve got to pump the water in. It has to be equal in pressure to the water outside the tube, not just full of water. The pumps are what makes the noise (well, half of it. The other half is just the doors clanking open or shut, but that’s less important because it’s a short noise. Whereas pumps are a sustained noise and thus trackable) ---
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [October 14, 2014, 12:02am UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/3 "2014-10-14T00:02:00Z")
> [@Kobal2](#): > > The tubes are filled with water \*before \*opening the doors. To equalize pressure - else they’d be really hard to open and make even more noise. High pressure water rushing in might even damage the torpedo, I 'unno. Ah, I see, total misconception on my part. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [October 14, 2014, 12:22am UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/4 "2014-10-14T00:22:26Z")
nm ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [October 14, 2014, 11:09am UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/5 "2014-10-14T11:09:26Z")
> [@Kobal2](#): > > The tubes are filled with water \*before \*opening the doors. To equalize pressure - else they’d be really hard to open and make even more noise. High pressure water rushing in might even damage the torpedo, I 'unno. > > As for how or whence to fill them : anyway you slice it you’ve got to pump the water in. It has to be equal in pressure to the water outside the tube, not just full of water. The pumps are what makes the noise (well, half of it. The other half is just the doors clanking open or shut, but that’s less important because it’s a short noise. Whereas pumps are a sustained noise and thus trackable) I had always assumed that you just open a valve to let the outside water in and another to let the air out into the sub. When water comes out of the air vent, it is full; the pressures would automatically equalise and the outer doors would open. Why would you need a pump? Of course after the torpedo was used, it would be necessary to pump the water out. ---
**Author:** ![Kobal2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kobal2/32/20_2.png) [@Kobal2](https://boards.straightdope.com/u/Kobal2)\ **Post date:** [October 14, 2014, 11:24am UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/6 "2014-10-14T11:24:23Z")
From [a page on German U-Boote](http://www.ubootwaffe.pl/en/u-boats/equipment/torpedo-tubes-of-german-u-boats) : > [@](#): > > The muzzle doors were necessary to prevent flooding the boat while reloading the tube. Outer torpedo tube doors opened against water pressure so that they were resistant to the high pressure at greater depth and explosions of depth charges. But even at periscope depth during submerged torpedo attack, the tubes were at a depth of ca 10 m, where the external pressure was about two times greater than the internal pressure and effectively prevented the opening of the muzzle doors. > That’s why the torpedo tubes had to be flooded before opening muzzle doors. There were two ways to do it: flooding with external sea water or flooding with water pumped from the special tank in the boat and equalization of the pressure by opening the hull valve connecting the tube with the sea. **The first case was a much simpler procedure, but during flooding there was a significant disturbance of the trim and a change in the weight of the boat.** In the second case the procedure was more complex, but during flooding the weight of the boat was not changed and the trim change was minimal (depending on the relative position of tanks and tubes). (emphasis mine) I have no earthly idea whether the same is true in modern subs, although I suspect the laws of physics haven’t changed overly much since then :). ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [October 14, 2014, 3:41pm UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/7 "2014-10-14T15:41:04Z")
The location-revealing noise isn’t from the tubes being flooded, its from the torpedo being ejected out of the flooded tube via high pressure air. That makes a whole lot of noise. The US was developing non-air ejected ‘swim-out’ torpedoes to counter this very problem. Don’t know if the project ended with the Cold War or not… ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [October 14, 2014, 3:49pm UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/8 "2014-10-14T15:49:15Z")
I think you’re on to something here. It should be trivially possible to build a quiet air compressor (that removes the air from the torpedo tube and compresses it into storage tanks) and a quiet valve that lets water into the torpedo tubes slowly and smoothly enough to avoid any noises revealing the action. This is a staple of Tom Clancy novels, where a pursuing enemy submarine is aware they are about to be fired on by the sound of the tubes flooding. Maybe it’s never been a problem. ---
**Author:** ![Kobal2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kobal2/32/20_2.png) [@Kobal2](https://boards.straightdope.com/u/Kobal2)\ **Post date:** [October 14, 2014, 5:12pm UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/9 "2014-10-14T17:12:28Z")
Theoretically you could flood tubes well in advance of any hostile encounter, though (in fact that’s the norm in sub sims - no idea how accurate that is). Other than possible long-term stress on seals and valves, and very slightly lower speed/manoeuvrability (since you’re pushing a handful extra tons of water you could not be) there’s not much of a downside; and one notable upside : you’re cocked, locked and ready to rock with minimal prep time. The doors opening/closing will probably always create some form of transient noise no matter how much rubber or springs are used to quieten them ; but that doesn’t really matter since opening the tubes in turn means you’re about to shoot something out, which will both a) make a lot of noise regardless (even if the firing process itself wasn’t noisy as hell as **Hail Ants** says, the torpedo’s own propeller would still be. Mk48s run between 30-55 knots or so with cavitation galore) and b) give whoever’s out there one \*very \*pressing focus of attention (or more) :). ---
**Author:** ![Ranger\_Jeff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranger_jeff/32/2065_2.png) [@Ranger\_Jeff](https://boards.straightdope.com/u/Ranger_Jeff)\ **Post date:** [October 14, 2014, 9:14pm UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/10 "2014-10-14T21:14:44Z")
You may not want to pump the water in a tube out of the tube after you fire a torpedo. After you shoot a torpedo, the bow of the sub will be the weight of one torpedo lighter and that can affect the trim. So there might be a tank in the bow they can pump the water from the closed at both ends tubes into. I don’t know if a tube full of water weighs the same as a tube, but it’s got to be closer than a tube full of air. ---
**Author:** ![iiandyiiii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/iiandyiiii/32/7924_2.png) [@iiandyiiii](https://boards.straightdope.com/u/iiandyiiii)\ **Post date:** [October 14, 2014, 9:21pm UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/11 "2014-10-14T21:21:19Z")
Modern torpedo tubes (at least for US fast attack submarines) are filled with water from the Trim and Drain system, which is the system of pumps and pipes that moves seawater around the boat for various purposes, chiefly to balance the buoyancy of the boat. Source – I was party of the crew of a US fast attack sub from 2004 to 2007. ---
**Author:** ![Hypno-Toad](https://avatars.discourse-cdn.com/v4/letter/h/b2d939/32.png) [@Hypno-Toad](https://boards.straightdope.com/u/Hypno-Toad)\ **Post date:** [October 15, 2014, 3:31pm UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/12 "2014-10-15T15:31:24Z")
> [@Kobal2](#): > > The doors opening/closing will probably always create some form of transient noise no matter how much rubber or springs are used to quieten them ; but that doesn’t really matter since opening the tubes in turn means you’re about to shoot something out, which will both a) make a lot of noise regardless (even if the firing process itself wasn’t noisy as hell as **Hail Ants** says, the torpedo’s own propeller would still be. Mk48s run between 30-55 knots or so with cavitation galore) and b) give whoever’s out there one \*very \*pressing focus of attention (or more) :). I wonder if there’s a way to silently “drop off” the torp then have it activate later. This could give the sub time to get away or at least change location enough that the launch will not give away it location. ---
**Author:** ![Ranger\_Jeff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranger_jeff/32/2065_2.png) [@Ranger\_Jeff](https://boards.straightdope.com/u/Ranger_Jeff)\ **Post date:** [October 15, 2014, 7:22pm UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/13 "2014-10-15T19:22:31Z")
> [@Hypno-Toad](#): > > I wonder if there’s a way to silently “drop off” the torp then have it activate later. This could give the sub time to get away or at least change location enough that the launch will not give away it location. Many are optical fibre guided now. One can shoot a torpedo at a slow speed from “under the layer” and guide it to where it’s close enough to lock on to the target and then turn it up to full speed and cut the wire. ---
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [October 15, 2014, 11:17pm UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/14 "2014-10-15T23:17:54Z")
> [@Ranger\_Jeff](#): > > Many are optical fibre guided now. One can shoot a torpedo at a slow speed from “under the layer” and guide it to where it’s close enough to lock on to the target and then turn it up to full speed and cut the wire. On a related note, I wonder if in tense peacetime, a nation could harass a submarine of a rival nation by having noisemaker limpet devices swim up silently to the sub’s hull, attach, and then emit loud continuous pings to betray that sub’s position for weeks or months. It would make that sub far easier to attack if an undersea cold war turned hot. Best of all, what if enemy ballistic-missile subs got “tagged” in the open ocean this way? ---
**Author:** ![Kobal2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kobal2/32/20_2.png) [@Kobal2](https://boards.straightdope.com/u/Kobal2)\ **Post date:** [October 15, 2014, 11:34pm UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/15 "2014-10-15T23:34:00Z")
> [@Velocity](#): > > On a related note, I wonder if in tense peacetime, a nation could harass a submarine of a rival nation by having noisemaker limpet devices swim up silently to the sub’s hull, attach, and then emit loud continuous pings to betray that sub’s position for weeks or months. It would make that sub far easier to attack if an undersea cold war turned hot. First of all, I think you need kind of a \*\*big \*\*thingamabob to make very loud pings ;). Secondly, the sub would just go to periscope depth (about 10-20 meters) and send away a diver to remove the thingamabob. Then cause a huge international incident by conclusively proving you aggressively, deliberately and with malice aforethought attached a thingamabob to one of their military vessels in peacetime - which is pretty much an act of war in and of itself :p. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [October 16, 2014, 8:21pm UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/16 "2014-10-16T20:21:14Z")
You could make the mine silent. It would passively listen for a coded sequence that would activate it to begin pinging. ---
**Author:** ![yoyodyne](https://avatars.discourse-cdn.com/v4/letter/y/a9a28c/32.png) [@yoyodyne](https://boards.straightdope.com/u/yoyodyne)\ **Post date:** [October 16, 2014, 8:22pm UTC](https://boards.straightdope.com/t/flooding-submarine-torpedo-tubes-from-the-inside/701250/17 "2014-10-16T20:22:25Z")
> [@Habeed](#): > > You could make the mine silent. It would passively listen for a coded sequence that would activate it to begin pinging. Or avoid the extra step and make it explosive. 🙂