# How does a diesl submarine engine "breathe?" **URL:** \ **Category:** Factual Questions\ **Created:** [October 13, 2008, 1:57pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709 "2008-10-13T13:57:14Z")\ **Posts on this page:** 7\ **Page:** 2
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [October 14, 2008, 3:53am UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/21 "2008-10-14T03:53:45Z")
It’s worth noting that even modern U.S. nuclear submarines have an emergency diesel generator (DG) and a snorkel mast that will allow the DG to be operated while submerged at periscope depth. The DG is required to be operated periodically for maintenance. During long operational exercises, it may be weeks or months before the DG can be started up. There’s nothing quite like being at PD or driving on the surface in heavy seas with the DG running and the wind causing the exhaust fumes to be drawn inboard. Add in the flapper valve periodically shutting and popping everyone’s ears, and you have a surefire way to get most of the crew puking their guts out. 😃 ---
**Author:** ![Noel\_Prosequi](https://avatars.discourse-cdn.com/v4/letter/n/b19c9b/32.png) [@Noel\_Prosequi](https://boards.straightdope.com/u/Noel_Prosequi)\ **Post date:** [October 14, 2008, 4:01am UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/22 "2008-10-14T04:01:48Z")
> [@Raguleader](#): > > The Swedes have an attack sub, the HMS _Gotland_, which uses tanks of liquid O2 to run the engines while underwater. They spent two years running circles around the US Navy off the West Coast as part of an ASW training program. > > [HSwMS Gotland (Gtd) - Wikipedia](http://en.wikipedia.org/wiki/HMS_Gotland_(Gtd)) > > Surely, if war ever finally breaks out between the US and the Swedes, we’ll get a heck of a bloody nose. 😃 I checked out the wiki site but it doesn’t seem to answer a question or two which occur to me - diesel/electric subs which only use the diesels on the surface can vent the exhaust without problems, and when underwater, there is no exhaust. But a sub which uses LOX while submerged to run diesels will have a whole heap of exhaust to dispose of. And just bubbling it out into the ocean is, to say the least, something of a giveaway. How do they dispose of the exhaust? And how do they keep the wraps on the noise of underwater diesels? ---
**Author:** ![Westrogothia](https://avatars.discourse-cdn.com/v4/letter/w/3ab097/32.png) [@Westrogothia](https://boards.straightdope.com/u/Westrogothia)\ **Post date:** [October 14, 2008, 5:54am UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/23 "2008-10-14T05:54:17Z")
> [@Raguleader](#): > > The Swedes have an attack sub, the HMS _Gotland_, which uses tanks of liquid O2 to run the engines while underwater. They spent two years running circles around the US Navy off the West Coast as part of an ASW training program. > > [HSwMS Gotland (Gtd) - Wikipedia](http://en.wikipedia.org/wiki/HMS_Gotland_(Gtd)) > > Surely, if war ever finally breaks out between the US and the Swedes, we’ll get a heck of a bloody nose. 😃 Well its a littoral sub so youll be fine if you stay out of the fjords. 🙂 ---
**Author:** ![dynamitedave](https://avatars.discourse-cdn.com/v4/letter/d/ed655f/32.png) [@dynamitedave](https://boards.straightdope.com/u/dynamitedave)\ **Post date:** [October 14, 2008, 6:48am UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/24 "2008-10-14T06:48:56Z")
> [@Noel\_Prosequi](#): > > I checked out the wiki site but it doesn’t seem to answer a question or two which occur to me - diesel/electric subs which only use the diesels on the surface can vent the exhaust without problems, and when underwater, there is no exhaust. > > But a sub which uses LOX while submerged to run diesels will have a whole heap of exhaust to dispose of. And just bubbling it out into the ocean is, to say the least, something of a giveaway. How do they dispose of the exhaust? And how do they keep the wraps on the noise of underwater diesels? One of the links on the wiki page gave a little more info. Seems the engines aren’t running underwater, the LOX and diesel run two 75kW Stirling cycle engines that allow two weeks submerged travel at 5 knots. They run in an inert environment (helium), I guess to prevent a fire or bang occuring. No comment about the exhaust though. I would of thought that any bubbles emitted would make a noise? However the amount of gas produced couldn’t be stored on board could it, i.e. compressed in bottles; too much energy and space required? So it has to be emitted, there has to be a silent way of farting deep under water 😛 I know I can in the bath 😃 ---
**Author:** ![VanillaGorilla](https://avatars.discourse-cdn.com/v4/letter/v/f9ae1b/32.png) [@VanillaGorilla](https://boards.straightdope.com/u/VanillaGorilla)\ **Post date:** [October 14, 2008, 6:55am UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/25 "2008-10-14T06:55:34Z")
> [@Noel\_Prosequi](#): > > I checked out the wiki site but it doesn’t seem to answer a question or two which occur to me - diesel/electric subs which only use the diesels on the surface can vent the exhaust without problems, and when underwater, there is no exhaust. > > But a sub which uses LOX while submerged to run diesels will have a whole heap of exhaust to dispose of. And just bubbling it out into the ocean is, to say the least, something of a giveaway. How do they dispose of the exhaust? And how do they keep the wraps on the noise of underwater diesels? I think they store the exhaust somehow, and then release it when they are sure no enemies are around. As for the engine noise, those engines are VERY quiet. They are some kind of Stirling engines, rumor has it that you can place a coin on its edge on top of the engine, and the coin will not fall over. I’ve stood right beside a sub when it left harbor, and it was almost completely silent, except for some splashing from the propellers, that would not be present when the sub was under water. ---
**Author:** ![slaphead](https://avatars.discourse-cdn.com/v4/letter/s/e9bcb4/32.png) [@slaphead](https://boards.straightdope.com/u/slaphead)\ **Post date:** [October 14, 2008, 7:00am UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/26 "2008-10-14T07:00:14Z")
> [@Westrogothia](#): > > Well its a littoral sub so youll be fine if you stay out of the fjords. 🙂 Sweden’s been a bit short of fjords ever since the norwegians ran off with most of the west coast. I think that particular sub is meant to spend it’s time sneaking about among the islands and inlets of the baltic coast, hopefully avoiding any [soviet-style diplomatic incidents](http://www.militaryphotos.net/forums/showthread.php?t=128144) ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [October 14, 2008, 7:29am UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/27 "2008-10-14T07:29:35Z")
You mean they’re pining for the… oh never mind. [Previous page](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709.md?page=1)