# Nuclear Submarines - Thermal Signature? **URL:** \ **Category:** Factual Questions\ **Created:** [July 20, 2011, 4:53pm UTC](https://boards.straightdope.com/t/nuclear-submarines-thermal-signature/589731 "2011-07-20T16:53:30Z")\ **Posts on this page:** 7\ **Page:** 3
**Author:** ![MichaelEmouse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/michaelemouse/32/101_2.png) [@MichaelEmouse](https://boards.straightdope.com/u/MichaelEmouse)\ **Post date:** [July 22, 2011, 4:51pm UTC](https://boards.straightdope.com/t/nuclear-submarines-thermal-signature/589731/41 "2011-07-22T16:51:19Z")
> [@muldoonthief](#): > > This sounds like a sub version of the [Fake bomb on the decoy airfield](http://www.snopes.com/military/woodbomb.asp) story. What would be the point of letting the Soviets know we could trail them? Perhaps getting them to abandon/deemphasize this particular means of nuclear weapons delivery? Even if the US was superior in this aspect, it might have disliked the use of nuclear weapons launching subs. ---
**Author:** ![Cabin\_Fever\_1](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cabin_fever_1/32/2908_2.png) [@Cabin\_Fever\_1](https://boards.straightdope.com/u/Cabin_Fever_1)\ **Post date:** [July 22, 2011, 10:08pm UTC](https://boards.straightdope.com/t/nuclear-submarines-thermal-signature/589731/42 "2011-07-22T22:08:48Z")
Wow. Let me apologize for being absent from this thread for so long. I certainly didn’t expect this many replies. Thank you all for the explanations to my query, and for all the extra tidbits about submarines. It certainly enlightened me in more ways than one. Thank you! ---
**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:** [July 23, 2011, 6:15pm UTC](https://boards.straightdope.com/t/nuclear-submarines-thermal-signature/589731/43 "2011-07-23T18:15:15Z")
> [@Blackhawk441](#): > > By all means, I cede to your expertise then. > > Just out of curiosity, what classes of subs did you serve on? I was a junior officer on an improved _[Los Angeles](http://en.wikipedia.org/wiki/Los_Angeles_class_submarine)_-class fast attack submarine. I also did a strategic deterrent patrol on an old _[James Madison](http://en.wikipedia.org/wiki/James_Madison_class_submarine)_-class fleet ballistic missile submarine. > [@Blackhawk441](#): > > About how long would it take to restart a reactor? I have trouble thinking of a situation where the reactor would have to be shut down yet would not cause enough permanent damage to allow it to be restarted. The most common reason a reactor is [scrammed](http://en.wikipedia.org/wiki/Scram) is for drills. Once the cause of the trip is determined (i.e “Reactor SCRAM due to [Chief] Engineer tripping the scram switch”), it can be rapidly restarted via a fast recovery startup. Other causes of reactor SCRAMs (or trips) include automatic SCRAMS caused by the protective equipment. Most often these unintentional trips occur (which does not happen very often) when the protective circuitry is being tested. :smack: Automatic SCRAMs can also be caused by failure of critical equipment (such as failure of a reactor coolant pump). In such cases, the reactor is designed to automatically shut down specifically to prevent damage to the reactor. In many cases, because U.S. naval reactors are also designed for robustness, operators can quickly shift to backup equipment and restart the reactor with little interruption. If the equipment casualty is relatively minor (such as an auxiliary pump), it is easy to switch to backup equipment without involving a reactor shutdown at all. ---
**Author:** ![clairobscur](https://avatars.discourse-cdn.com/v4/letter/c/839c29/32.png) [@clairobscur](https://boards.straightdope.com/u/clairobscur)\ **Post date:** [July 23, 2011, 7:46pm UTC](https://boards.straightdope.com/t/nuclear-submarines-thermal-signature/589731/44 "2011-07-23T19:46:12Z")
> [@wevets](#): > > The French seem to have a number of nuclear attack submarines of the [Rubis class](http://en.wikipedia.org/wiki/Rubis_class_submarine) - do you mean that they run them without the reactor or ? I mean that I was mistaken Sorry for the non-factual statement and the spreading of some of my ignorance..☹ ---
**Author:** ![clairobscur](https://avatars.discourse-cdn.com/v4/letter/c/839c29/32.png) [@clairobscur](https://boards.straightdope.com/u/clairobscur)\ **Post date:** [July 23, 2011, 7:57pm UTC](https://boards.straightdope.com/t/nuclear-submarines-thermal-signature/589731/45 "2011-07-23T19:57:53Z")
> [@clairobscur](#): > > I mean that I was mistaken > > Sorry for the non-factual statement and the spreading of some of my ignorance..☹ Worse than that : after checking, there’s _no_ non nuclear French submarines. Don’t know where I picked the false info. Sorry again. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [July 23, 2011, 11:16pm UTC](https://boards.straightdope.com/t/nuclear-submarines-thermal-signature/589731/46 "2011-07-23T23:16:14Z")
> [@TriPolar](#): > > There appears to be [something](http://www.atimes.com/atimes/China/LE13Ad02.html) to this. But it could still just be something we want others to believe. My Google-Fu is failing me. I am sure I have heard the story that the US did this. I am pretty sure I heard Tom Clancy relating this story. Yes he is a writer of fiction but my recollection is this story was true. As to why we’d do this it was supposedly a message Reagan wanted to send that we had the Soviets number in this respect. The Soviets of course had spies in our government and their sub driver probably knew they were often followed. I am not sure there was a big secret that this happened (as noted the Soviets took to using the Crazy Ivan maneuver to try and shake US subs pursuing them). Pinging all soviet subs at the same time sent a message loud and clear that we had their number. It may seem silly but if they kind of already knew this was the case the effect is more a punctuation mark to a message than anything else. Also, knowing you are being followed doesn’t change much in this respect so it is not messing things up for the US sub drivers. ---
**Author:** ![Blackhawk441](https://avatars.discourse-cdn.com/v4/letter/b/76d3ee/32.png) [@Blackhawk441](https://boards.straightdope.com/u/Blackhawk441)\ **Post date:** [July 25, 2011, 6:22am UTC](https://boards.straightdope.com/t/nuclear-submarines-thermal-signature/589731/47 "2011-07-25T06:22:38Z")
> [@robby](#): > > I was a junior officer on an improved _[Los Angeles](http://en.wikipedia.org/wiki/Los_Angeles_class_submarine)_-class fast attack submarine. I also did a strategic deterrent patrol on an old _[James Madison](http://en.wikipedia.org/wiki/James_Madison_class_submarine)_-class fleet ballistic missile submarine. > > The most common reason a reactor is [scrammed](http://en.wikipedia.org/wiki/Scram) is for drills. Once the cause of the trip is determined (i.e “Reactor SCRAM due to [Chief] Engineer tripping the scram switch”), it can be rapidly restarted via a fast recovery startup. > > Other causes of reactor SCRAMs (or trips) include automatic SCRAMS caused by the protective equipment. Most often these unintentional trips occur (which does not happen very often) when the protective circuitry is being tested. :smack: > > Automatic SCRAMs can also be caused by failure of critical equipment (such as failure of a reactor coolant pump). In such cases, the reactor is designed to automatically shut down specifically to prevent damage to the reactor. In many cases, because U.S. naval reactors are also designed for robustness, operators can quickly shift to backup equipment and restart the reactor with little interruption. > > If the equipment casualty is relatively minor (such as an auxiliary pump), it is easy to switch to backup equipment without involving a reactor shutdown at all. Very interesting, thanks for the reply. Figures that the nuclear circuit breakers (band name!) would trip the most while testing it. At least they left them on, unlike Chernobyl :smack: [Previous page](https://boards.straightdope.com/t/nuclear-submarines-thermal-signature/589731.md?page=2)