My first thought when I read How can I hide my island? was that if the villain is being tracked by satellite imagery, they should just go to the island via submarine. But then I realized I don't actually know how easy it is to hide using a submarine.

So, how hard would it be to track someone who is trying to disappear using their own submarine?

I can think of two technologies for tracking off the top of my head (as well as questions about their limitations):

  1. Satellites. How deep would they have to go before satellite imagery wouldn't show their submarine? Are there different kinds of satellites that might force them to go deeper in order to remain undetectable? How far would they have to travel at depth in order for your satellites to have very little chance of being able to find them again?
  2. Sonar. Is there a maximum range for sonar? Are there any submarine-tracking systems in existence, such as an array of sonar detectors spread out over a large area? If none exist, how expensive/difficult would it be to set one up?

What other technologies are there that could be used to track a submarine? What limitations do they have?

I would appreciate hard-science where possible (such as how deep to avoid satellite imagery). I don't expect classified-info levels of accuracy, but we should be able to narrow it down with non-classified info. For example, light doesn't reach to the midnight zone (1000m deep), so if the sub could travel there it obviously wouldn't show up on a satellite image. I'm sure we can do better than that number, though.

Near-future tech is also okay as long as you are clear that it doesn't exist quite yet.


closed as off-topic by Mołot, sphennings, L.Dutch, Azuaron, Vincent Jul 10 '17 at 15:00

This question appears to be off-topic. The users who voted to close gave this specific reason:

If this question can be reworded to fit the rules in the help center, please edit the question.

  • 6
    $\begingroup$ One challenge here: the hard-science you want is almost certainly all in classified documents regarding nuclear submarines. Rest assured, the nations which have such submarines have a vested interest in you not knowing the answers to these questions =) $\endgroup$ – Cort Ammon Apr 20 '17 at 19:30
  • 1
    $\begingroup$ @CortAmmon that doesn't surprise me. That's part of the reason why I didn't use the hard-science tag. However, it wouldn't be too unreasonable for someone to look at diffusion of light underwater and determine the depth at which light would be too scattered to notice a submarine. $\endgroup$ – Rob Watts Apr 20 '17 at 19:34
  • 1
    $\begingroup$ @Mołot Actually, I was quoting the second to last sentence. You are correct about the tag: I also see it as science based $\endgroup$ – Cort Ammon Apr 20 '17 at 19:34
  • 4
    $\begingroup$ Read The Hunt for Red October. It's somewhat out of date, but it's a good starting point and a lot of fun. $\endgroup$ – MissMonicaE Apr 20 '17 at 19:35
  • 2
    $\begingroup$ Also, sonar is limited not just by range, but by the fact that ocean temperature is different at different depths, and sonar waves can bounce off the boundaries between different temperature-layers, so you can hide from someone in one layer by staying in another. $\endgroup$ – MissMonicaE Apr 20 '17 at 19:37

Magnetic Anomaly Detectors

enter image description here

MAD devices detect the interaction of a moving submarine's hull with the Earth's magnetic field. As such, they can be used to track a submarine underwater as long as it stays on the move and doesn't go too deep (although MAD works pretty deep, deeper than sonobuoys I can tell you from experience, though specifics are obviously classified). A regular diesel submarine would probably not have the diving capability to avoid the P-3's, so the only way your villain gets away is if he has hijacked a US or Russian nuclear sub (possibly a Chinese one; I don't really know how good those are).

MAD booms can be mounted on patrol aircraft with very long times in the air, such as a P-3 that can do an 8 hour patrol easily. A pair of P-3's and bases to refuel at, and you could track a submarine all the way around the world.

So basically, the US Navy can track him all the way...if they found him in the first place. The thing with MAD is that it is relatively easy to track the movement of someone you know is there, it is relatively hard to find someone just by running the plane back and forth across the ocean. If the goal is for the villain to get away, then he just needs to escape notice for a few hours, then he will be as easy to find in the open ocean as a needle in a haystack.

Regarding satellites, a satellite will never find a diesel submarine that is either underwater or snorkeling on diesels. You have no reason to be on the surface if you are trying to hide, so a satellite will not find you,. Regarding sonar, a passive sonar will never find a submarine that is running on electric. Since I assume your submarine has its own sonar, the solution is simple: run snorkeling on diesels when there is no-one else around, and run submerged on battery when there are other ships nearby.

If you did that, the chances of being found are close to nil, and totally random. The ocean is huge, and the chances that an aircraft would randomly fly over head while you were snorkeling and spot your snorkel (they are small) is not very big. The chances that a passive sonar having ship will sneak up on you close enough so it get a range on your diesels is also not very big.

Conclusion: it is pretty easy to hide in a submarine, and as long as you don't get tracked right out of the harbor it should be fairly trivial to get to your secret island/resort undetected.

  • $\begingroup$ Could a sub hide from MAD by traveling below a commercial shipping vessel? Or would the vessel itself through off enough active sonar to "light up" the sub? $\endgroup$ – CaM Apr 21 '17 at 13:24
  • 1
    $\begingroup$ @CM_Dayton Yes, you can hide from MAD that way, or at least make it much harder to track you. However, I suspect the Navy would firmly instruct the merchants to stay out of the way, and also a submerged non-nuclear submarine can't keep up with a merchant (they usually are going 18-22 knots, way too fast for a diesel sub). Even a nuclear submarine would make enough noise to be easily tracked by keeping up with a merchant ship. $\endgroup$ – kingledion Apr 21 '17 at 13:27
  • Satellites.

    Satellites can detect submarines in various ways. Commonly they are used to detect the wakes of moving submarines; going deep will help the submarine avoid this, but in many places of interest the sea is just not that deep. For example, the Taiwan Strait is only 70 meters deep. Water is also pretty transparent; going deep will help here too. There are also rumors of other methods, such as ultra-sensitive gravity gradiometry or magnetometry, but they seem more science-fiction than practical. But then, a lot of military tech seems more science-fiction than practical until it becomes ordinary.

    On the other hand, various powers spend a lot of money and effort in detecting submarines from aircraft, which are much closer to the sea than satellites.

  • Is there a maximum range for sonar?

    Yes. Hard numbers are hard to come by, but active sonar is commonly thought to be limited to a few kilometers (say, maybe 6 km or at least on this order of magnitude). Passive sonar performance depends on many many factors, so that sometimes it can detect noisy submarines at hundreds of kilometers (see SOFAR channel), and other times it will miss modern submarines at 5 kilometers. If the passive sonar is aboard a moving submarine or surface ship it may even miss modern submarines at closer range. Modern submarines are very very quiet when they move slowly.

    On the other hand, detection techniques are evolving fast. See the article "Transparent Sea: The Unstealthy Future Of Submarines " by Sydney J. Freedberg Jr. at Breaking Defense (2015).

  • Are there any submarine-tracking systems in existence, such as an array of sonar detectors spread out over a large area?

    SOSUS (short for sound surveillance system) is a chain of underwater listening posts located around the world in places such as the Atlantic Ocean near Greenland, Iceland and the United Kingdom—the GIUK gap—and at various locations in the Pacific Ocean. The United States Navy's initial intent for the system was for tracking Soviet submarines, which had to pass through the gap to attack targets further west. It was later supplemented by mobile assets such as the Surveillance Towed Array Sensor System (SURTASS), and became part of the Integrated Undersea Surveillance System (IUSS). (Wikipedia)

    Japan has a similar system too.

Hiding a nuclear submarine long-term is obviously easier than hiding a conventional submarine which needs must come to the surface to recharge its batteries. On the other hand, on a shorter term a conventional submarine can hide better than a nuclear submarine because it makes much less noise and it is (or can be) much smaller. If you want to be amazed at the state of the art in conventional subs, look at the German Type 212:

In 2013, while on the way to participate in naval exercises in U.S. waters, the German Navy's U-32 established a new record for non-nuclear submarines with 18 days in submerged transit without snorkelling. Also it got through all the defence of a U.S. carrier strike group, unseen, and shot green simulation torpedos at the carrier. (Wikipedia)

  • $\begingroup$ Interesting AlexP. Do you have any links to that exercise or where you found that info? Would like to read about that for sure. $\endgroup$ – ggiaquin16 Apr 20 '17 at 21:11
  • $\begingroup$ @ggiaquin: It's taken from the linked Wikipedia article; unfortunately the link given in the relevant footnote is no longer valid. But with great effort I managed to find a nice write up in Undersea Warfare under the title "German submarine deploys to U.S. for WESTLANT 2013" by Cmdr. (sg) Sascha H. Rackwitz. $\endgroup$ – AlexP Apr 20 '17 at 22:12

The answers by AlexD and kingledion both assume that the submarine is a modern state of the art military boat, but there is much more to it than that.

The Soviet era Alfa submarine had a Titanium hull, which is non-magnetic and much harder to detect with magnetic anomaly detectors, effectively making them useless. However, as submarines go, while very fast, it was also noisy, which is the last thing a naval submariner wants.

So, if MAD is rendered irrelevant, and since optical observation - either visible or infra-red - by aircraft or satellite is dependent upon the submarine remaining above the Secchi depth, which at sea is between 1 and 50 metres, most typically around 20m in the deep ocean, but less in more coastal and disturbed areas, any submarine capable of submerging below 50m or whatever the local Secchi depth is can go unseen.

Similarly, water attenuates radar severely at the frequencies typically used for surface search and tracking, making these radar sets useless for underwater search. Low frequency radar can penetrate water effectively, but even aboard a ship the antennas required are impractically large.

This leaves only sonar. Water transmits sound extremely well - but all sounds, not just those of submarines. There is a constant background noise into which a submarine may vanish if it is quiet enough. Modern submarines detect each other using waterfall displays, where the width of the screen represents the unwrapped 360° space around the sub, and the vertical axis represents time, with the current time at the top. With no contacts, the waterfall display shows random dots, but a noise-emitting contact results in a line, vertical if it is at a constant bearing, otherwise it is slanted from the vertical. The sonar operator can select a contact and use a frequency spectrum analyser to split the sounds emitted by a target into discrete frequencies over time, and finally, the sonar operator can listen to the contact.

Man-made objects such as ships and submarines have distinctive sounds that separate them from geological and biological sounds. Ships and subs usually have propellers, and sonar can - when close enough - detect the individual blades as the screw turns as a kind of beat. The faster the screw is turning, the louder and easier it is to detect, as the blades cause cavitation once the blades are travelling through the water fast enough. A vessel can be tracked by guessing its type from its sound, calculating a blade-rate, guessing (or hearing) the number of blades based upon the probably type of contact - if the propeller is worn or damaged, determining the number of blades can be achieved from observation since each blade takes on a distinct sound of its own - and then guessing (or knowing from prior experience) the speed-per-RPM and calculating the probable speed. From that, and knowing the movement of one's own submarine, a reasonably exact course can be determined for the contact over a period of time, perhaps 15 minutes, since the bearing at each moment will be known, and the probable speed can be used to fit the course with time markers to the observed bearing to the target at those times. By moving the proposed course around until its time markers match with the bearing at those times, the actual course can be determined. Choosing an inappropriate speed can be detected using this method, since it will usually result in the appearance of a curved course, while most ships travel in straight lines for the most part.

So, in a break-away contest, we have the villain's submarine and we can assume the pursuer's. The villain would want as quiet a sub as he could manage - let's hope he hasn't gone with a noisy soviet-era nuclear clunker unless he's spent a fortune refitting it. Nuclear subs are actually noisier - they sound like a kettle on the boil - whereas diesel-electrics are much quieter except when snorting to recharge their batteries. Some modern subs only emit sound below ambient when running silent and at low speed, these would include US missile submarines and some new diesel-electric subs. However, at close range, even emitting below ambient isn't necessarily going to help against a pursuer with experienced sonar men and state-of-the-art sonar transducers - they can see the shadow the fleeing sub makes in the background noise, as well as hear the distinctive mechanical sounds.

However, that isn't all there is to it. A fleeing sub can use decoys to produce the sounds that the pursuer is expecting to hear in a place other than that where the pursued is, or to simply fill the water with bubbles that mask the sounds beyond it. The water temperature typically decreases somewhat as depth increases, but there are also strata of temperatures within the seas, with thinner strata across which temperature changes rapidly, known as thermoclines, which - because they refract sound - can be used to hide from an enemy. Some locations have multiple thermoclines, or there may be only one, or none at all in shallower areas. Consider the confusion caused upon the pursued dropping a moving decoy above a thermocline, then ducking beneath that thermocline and changing direction. Some sonar crews may fall for the deception, and continue to report the incorrect course that the decoy is taking rather than reporting that the target has changed depth and released a decoy.

Changing depth has its own acoustic signature - a creak or groan as the pressure upon the hull changes, resulting in it expanding or contracting. Launching a decoy or torpedo may be heard, since these devices are loaded into dry tubes that are then flooded - with a sound like that of a toilet flushing - the tube doors opening, with associated mechanical sounds, and then a shot of high-pressure air to eject the device, again with a distinctive sound, much louder in the case of torpedoes than decoys. Some torpedo-tube launched mobile decoys are "swum" out, being launched without the shot of high-pressure air to keep things quiet.

In detection and evasion exercises between submarines, a sonar telephone is typically used to announce the administrative launch of a torpedo, but it is also known for a torpedo tube to be fired empty, particularly where the participants in the exercise are not all that friendly, to wake up a negligent ally, or to flush out a lurking enemy. The distinctive sounds of a torpedo tube being flooded, opened and fired are much like the sounds of a pistol being cocked are to a land-dweller, or even worse, since they represent not just the weapon being armed but actually fired, and it takes an experienced sonarman to be able to tell the difference between a loaded tube and an empty tube being flooded and fired. Also, since the firing of a tube releases a mass of bubbles, the torpedo engines won't be heard for a second or two, and any decently-trained sonar man will report a torpedo launch on hearing the first sounds without waiting to hear the torpedo, since seconds can make the difference between life and death when attempting to evade a torpedo.

Evading a torpedo is possible by going to maximum speed, releasing a decoy (often static) and then changing direction, hoping that the torpedo sonar will acquire the decoy's bubble cloud rather than the sub while the sub heads in another direction. A counter-attack shot down the line of bearing to an enemy torpedo may be useful to get the attacker to cut the guidance wires to their own torpedo in order to maneuver - an unguided torpedo has to rely upon its own limited brains rather than those of a human crew while its guidance wire is stall attached, and a miss is more likely when unguided, since a crew can both listen through and manually control the torpedo while on the wire.

So, a torpedo launch, whether real or dry, is cause for a submarine to go to full, noisy, power, and it takes experience to know if the launch might be a bluff which can be ignored, or is a potentially deadly attack which must be evaded. An evading submarine can be made to reveal its presence by going to full power, but on the other hand, an evading sub may also launch a live torpedo or dry-fire a tube in order to get their pursuer to go to full speed, since at higher speeds, flow noise degrades sonar performance, giving the pursued a chance to vanish into the background noise while the pursuer is running and can't hear.

It is of interest that drug cartels are now building single and multiple-use submersible craft to smuggle drugs. These narco-subs are increasing in sophistication, but have also led to laws - in the US at least - outlawing the use of an unflagged submarine in international waters, so the OP's villain had better have a pretty good sub, or at least have a registered sub and a good excuse to be using it in the event of capture.

If we're talking about a James-Bond style villain with heaps of ill-gotten gains and global contacts in the right places, his submarine could well be an all-up torpedo-armed sub of a quality equivalent to the best in the world, something that even the US authorities would have difficulty tracking and capturing, or it may be a more improvised affair, a-la the Columbian narco-subs.

So, as I've shown, the "range" of sonar depends upon all sorts of things, and can't really be expressed as a hard number. An advanced submarine evading a poor pursuer may not be detectable at a few hundred metres range, or the other way around, may be detectable a hundred kilometres away. Given technical parity, a realistic detection range might be ten to thirty kilometres, and even that depends upon the skills of the respective crews. Also consider that detection and capture are different things - when we're talking about armed subs, a single torpedo is a game-changer - if our villain launched just one real torpedo, with a decent motor, range and sonar seeker, it would scare the opposition into handling the situation far more conservatively regardless of wether the torpedo did any actual damage, and potentially allow the villain to escape.

On the other side, many first-world nations have emplaced sonar networks. The G-I-UK SOSUS net that runs from Greenland to Iceland to the UK was emplaced to detect soviet submarines, and while effective, was never infallible. Local sea conditions can reduce sonar performance, the sub captain's patience and knowledge could lead him to creeping past the sensor net so slowly that the sub just isn't heard, or the sub captain could use a convenient merchantman as a hat, travelling beneath it in order that the sub's signature be lost amongst the merchantman's noisier signature.


If competent authorities know WHEN and WHERE the villain starts his escape in his submarine, AND has resources in place, then it is extremely difficult to stay hidden, even in a submarine.

  1. Passive sonar systems are very good and widely distributed across key parts of the ocean floor, or can be dropped via aircraft. It is highly unlikely that a villain would have access to a super-stealthy submarine, although the new non-nuclear AIP subs from Germany can be extremely stealthy without all the trouble of needing a nuclear reactor.

  2. Satellite and airborne systems can track subs via several methods, IF they know where to look. They can detect the phosphorescent wake left by a passing ship through plankton swarms, use blue-green lasers (which can penetrate water) as a LIDAR system, and measure the water displacement of the sub on the surface, even if it is deep. The MAD system is already described here.

  3. They can place hunter/killer subs AHEAD of the villain, at places he is likely to cross. The faster he goes, the more noise he makes, the easier it is to detect him if you are already in an intercept position. They could even place nuclear mines in these places, set to depths far below other marine traffic, to deny the villain the ability to escape.

  4. Hiding amidst commercial traffic only works if the villain can get into the traffic flow at an unknown time and place. Otherwise the most likely masking vessels (which are usually not very close together out in the open ocean) can be easily tracked and diverted into places where the hiding villain can be easily flushed out and captured/destroyed.

So, in short, a submarine escape is actually rather difficult, if the good guys have resources in place. Obviously escaping from the shores of Africa, far from airbases, ASW forces, and pre-positioned naval assets would be much easier than escaping from a well defended place such as New York City. Much of the stealth value for a sub comes from not knowing when and where they may be, not in the inherent camouflage nature of the vessel itself (although the technological bar to detect a sub is fairly high).


In addition to the perfect answers from @AlexP and @kingledion there are some options to hide the submarine:

  1. Go underneath the ship.
    • The noise from its engines hide the submarine from any sonars
    • Satellites and airplanes can't see the submarine too
    • You could do this only for several hours - and it's almost impossible to track your submarine.
  2. Use the ship as a base.
    • The submarine re-fuels and the crew takes a rest on the ship
    • Secret passengers and cargo could travel mostly by ships: submarine->ship->submarine->another ship.

So nobody could track the route and nobody could say Definetely he went to the secret island. At most someone could say we don't know where he is. At least anybody would think He's on the sea travel.

These ways are real and have been used during the Cold War.

It's almost impossible to track someone everywhere who has proper organisation and enough money. Note that somewhere (like the Panama channel) you can't escape the tracking.


It is the very mission of a boomer to disappear at sea. To some extent they can be trailed when their location is known (for example, when leaving base) but noise in the water can be used to confuse a sub trying to chase them.

If the boomers weren't able to do this we wouldn't consider them a very important aspect of our nuclear deterrence.

Magnetic anomaly detectors have been mentioned in other answers. You have to get close to use them--and they work very poorly against titanium-hulled submarines.

About your best bet is a fleet chasing him with a bunch of helicopters but even that isn't anything like assured if he's got a nuclear sub, especially if he's willing to be obvious about getting away. (For example, jettison a large explosive device, detonate when he's far enough away for safety. Every sonar in the area is temporarily jammed.)


Depending on your flexibility with timeline and such, it is believed that a sufficiently sensitive neutrino detector would be able to track the location of any nuclear reactor on earth.

With current tech, this method is not possible since neutrinos are notoriously hard to detect since their interaction with "normal" matter is extremely weak. Experiments have been running for a few years and they've only detected a handful.

This article elaborates and shows what such detector might see:



Not the answer you're looking for? Browse other questions tagged or ask your own question.