https://en.wikipedia.org/wiki/Pathfinder-class_survey_ship
there is also the danger that a drone emitting sonar pings may be indistinguishable to a third party from a live torpedo, and makes it look like you're preparing to attack somebody you really don't want to start a war with (China, etc).
Any active sonar would likely paint the submarine anyway too for any passive sonar listeners.
Overall, unlikely to be useful.
How would it be useful to them at that distance?
The drone can transmit the ping and the sub can listen.
If I'm hiding in the darkness I can send a drone out with a lightbulb to shine a light near what I want to see without revealing myself.
And how would the drone know to 'flash the flashlight' where it was useful to the sub without the sub somehow communicating to the drone? Which would require the sub to emit something.
If it was programmed into the drone when it was launched, just the drone coming to and from the sub would draw a giant red line to and from the sub. It would also severely restrict the sub - it either has to program in a path, in which case the drone will illustrate where the sub WILL BE shortly, or it has to do a one-off, in which case anyone could listen to/follow the drone back to the sub when it's retrieved.
Seems not very useful in practice, except as some kind of disposable thing during an attack for redirection or distraction.
A programmed path wouldn't illustrate where the drone or sub will be in advance so that's also a non-issue. You only know where the ping came from, at the time the ping was sent.
The drone could also simply surface and pick up new instructions from satellite.
I assume we will soon be moving en masse to underwater drones for reasons far beyond what's discussed here.
There are of course ocean based drones already, but they tend to be for surveillance and data gathering in general - like detecting subs. Not so much for navigation.
But, I hope we do agree without question that it's possible, should we wish to do so.
Fire and forget programmable torpedoes have been a thing for decades.
What makes no sense is trying to link them in some operational/controllable/recallable way to submarines which are trying to remain covert, as the communication channels give away the submarine or require them to do risky behaviors like surface for satellite comms.
So my point is, you’re not proposing anything novel where you seem to think you are, and where you think they are advantages are actually significant operational disadvantages based on actual submarine mission profiles.
Step 1. Have a thousand cheap solar (or buoyancy/wave) charged sonar drones spread over hundreds of miles.
Step 2. Have a hundred silent listening drones spread over the same area.
Sonar drones can tell anyone and everyone that they exist and where they are, and encrypt what they see to transmit over whatever channel.
Listening drones learn what the sonar drones saw by whatever means (satellite, VLF radio, etc).
One of them gets close enough to the sub to tell it. The others all whisper into the void somewhere.
Or the sub just listens directly if it's close enough.
There's probably some better way of the sub learning what's around it that's top secret though
The big issues tend to be:
1) active sonar plays havoc with marine life, and it’s not a problem that can be typically solved by shifting frequencies, as the frequencies used by certain species are used due to beneficial transmission characteristics.
Wartime sonar is so powerful it can literally kill or injure people or animals nearby in the water due to the over pressure pulse, so tends to be seen as dangerous and undesirable to use except in specific emergency circumstances.
Low energy active sonar is indeed used by a lot of folks, but due to #3, would likely have some economic issues.
2) sound can be listened to in the oceans over far longer distances than a useful return signal can be gleaned by the emitter, and tends to transmit unevenly due to factors that are difficult to impossible to predict or control like thermoclines, currents, etc. [https://oceanservice.noaa.gov/facts/sound.html]
Listeners to an active sonar emitter can identify the location of something using triangulation even 10-100x the distance the ‘pinging’ party could get a useful return signal. (See performance here [https://en.m.wikipedia.org/wiki/Sonar]. Think of it like shining a flashlight around in the dark. Folks miles around could see the pinprick of light easily, even if the flashlight wielder can see nothing out there, and it’s not bright enough for everyone else to see anything else either.
Listeners at 2x the distance would typically have the same clarity of view as the initial ‘pinging’ party within the area energized.
This also makes it easy to avoid for parties trying to hide. They stay 5x the distance from the active sonar, and they’re likely good, minus passive sonars listening for engine noises or whatever which are always a hazard.
And 3) distances in the ocean are huge. Much, much larger than you might be mentally modeling.
Outside of a harbor or port (which generally already have these systems), a hundred square miles of ocean is tiny.
The Atlantic Ocean is 41.2 million square miles, the pacific 63.8, and the Indian Ocean 27.
So covering any useful segment of a large shoreline can be nearly impossible economically, let alone a segment of the open ocean. Even if you wanted a sensor per 100 square miles over half of the ocean - say the most interesting/busy parts of the ocean, or approx. 70 million square miles, well, 700k drones are not going to be easy to build, maintain, etc.
For this reason, equipment tends to be carried by parties who might need it, and only deployed in areas they might need it, or deployed as fixed installations in very high value/interesting areas.
Sonobouys from helicopters, sonar arrays on ships or submarines, fixed sonar installations at harbors, ports, clandestine passive sonar arrays near expected strategic areas off coastlines, etc.
4) clandestine bandwidth is very limited.
VLF has VERY low bandwidth (depending on frequency), so low even voice transmission is generally not practical, and it still has limited penetration into water. As far as I am aware, it’s used the equivalent of submarine texting (at best), and the submarine still has to come quite close to the surface. ELF can work at operating depths, but communication is one way, and bandwidth is in the ‘bits per minute’ range [https://en.m.wikipedia.org/wiki/Communication_with_submarine...]
ELF antennas are measured in miles and use the earths crust.
Sound in the ocean has weird transmission effects. If your quiet ‘whispered’ data gets under a thermocline, it could go 100s of km and you would be none the wiser. If it didn’t, it might go just meters. Distortion at high frequencies also makes it difficult to transmit much data this way unless the listener is close.
You’d want some kind of mesh network ideally though, as whatever node the sub is near would not be one the sub would want to approach if there was a potential enemy contact nearby, as it’s drawing a giant target on them.
If one way, that could be useful - however that also means the crypto better be really good, as one compromised node would turn the array into an enemy asset to hunt your subs, and the passive listening and mesh network model would mean you’d need to be transmitting all potentially interesting data all the time.
This sounds exactly like the kind of thing a top secret military program would know how to do with a few petaflops of calculating power, a network of linked microphones, and a complete survey of the area. At least to ranges that would be very surprising to someone outside of that program.
But yes, anything some rando on hn thinks of in five minutes has been thought of and dismissed or thought of in detail and had problems said rando didn't think of worked through.
I haven't suggested any novel ideas at all. I'm only pointing out something that should be obvious.
This conversation started when someone asked whether it's possible to use sonar without giving away a sub's location. It is possible. That's really all there is to it.
If doing the equivalent of dropping a speaker into the ocean and giving a speech, yes it is possible of course.
This might be an interesting paper - https://www.researchgate.net/publication/340683649_Cellular_...
Covering specific physics reasons, alternatives, etc.
Yes of course. No one has suggested otherwise. That's the entire point of using a drone, after all.
They couldn’t control something that they can’t talk to without giving away their position?
No, it would not. We already discussed this above, vis a vis preprogrammed paths.
I don't really want to rehash things we've already discussed. Have a good one.
Not to mention that sonar is highly disruptive to many forms of sea life as it's incredibly loud.
Or something thermal sensor based, there's rumored to be systems that submarines can use passively to follow and track other submarines by the waste heat put into the water.
https://en.wikipedia.org/wiki/SQUID
Managing the interference is probably the main issue.
Actually, I see now the Wikipedia entry lists prospecting among the uses, so I guess it's quite possibly not only practical but even practiced.
The main problem in using it, as I understand it, is rather that picking up everything the sensor could detect would usually result in an unmanageable deluge of unwanted information, and it's a normal operation context to filter the signal for distance so as to not pick up too much interference from equipment, staff, etc. But personally I don't see any reason it would be impossible to arrange it to band-pass instead of low-pass in that filtering.
Submarines go to great lengths to be as quiet as possible so that the acoustics of the engine, ship, etc. can't be caught in a microphone. Any sort of EM radiation is child's play to trace compared to that. The content of the message and the frequency of the message don't matter - any sort of signal means you can be monitored and your location determined.
You're right in that a broadcast is required, but I don't see why the broadcast should have to come from the sub itself.
While water motors are not exactly my area of expertise, I would also expect that drone/torpedo motors are significantly louder than submarine engines and that launching or recovering a drone is itself a fairly noisy event that exposes the sub to traditional acoustic tracking.
In terms of noise, keep in mind that submarines have all sorts of concessions already. A diesel-electric sub is quieter than a nuclear sub, but it has to surface every two days or so to get air to run its very noisy diesel generators.
I think a battery powered electric drone should be far quieter than any sub technology we have (steam/nuke is loud, diesel is louder). The quiet systems we have are all electric and therefore have limited energy capacity.