I read today that during World War II, depth-charging often carried a drawback which was that the turbulence caused by the underwater explosions made sonar effectively useless for up to 15 minutes after the charges went off. Could small, harmless depth charges be used, or is it already used, by modern military submarines, to make a getaway when being pursued? Just set them off at a safe distance, let them blind enemy sonar, and move away while the turbulence is still doing its thing.
Then the submarine wouldn’t be able to “see” either as they use sonar as well.
In theory, if a system was developed with enough sensors for dead reckoning, you could plot the course, fire the depth charges and make a run for it. In deep water this probably would work. In shallow water the sub might run aground.
However, once you are out of the affected area you would be able to be detected again. I guess you could have rear-firing charges that are timed so as to minimize the effect on the sub sonar. But that’d be tough as water isn’t considered to be compressible and the shock wave would travel faster than the sub could ever go.
Not saying it can’t be done, just this is a very complex problem.
Don’t they have already have, as a commentator put it, “Giant Alka-Seltzer tablets,” to fill the surrounding areas with bubbles? Plus there are autonomous decoys, towed decoys, and (finally), a counter-torpedo torpedo. The article mentions surface ships, but why couldn’t it also be used on subsurface platforms: The Navy Is Quietly Arming Its Supercarriers With Anti-Torpedo Torpedoes
There seems to be an implication that submarines use sonar to navigate. This is not the case. No submarine would be willing to transmit a signal (active sonar) during normal operations and certainly not while under attack. That would be suicide. Submarines navigate by dead-reckoning and inertial navigation systems-and I am sure several passive systems that no one outside the service talks about. But it isn’t sailing through the water pinging away. They do use recordings of natural sounds-quakes seem to be popular-for communication and depth finding, but not for looking out for obstructions.
See: https://www.warhistoryonline.com/military-vehicle-news/uss-san-francisco-crashed-2.html
If I may, an off-topic but possibly related question.
How close to its submarine target would a low yield nuclear torpedo (e.g. the Mark 45) have to detonate to kill it (its CEP if you will)?
Whatever that distance was, in a real shooting war that’s how far away a Soviet sub commander would need to get from his USN adversary.
But your trail of explosions will give a general idea of where you are and the direction you are going.
Sure, but (in theory) it would prevent the enemy from getting a good firing solution on you. It would be akin to soldiers using smoke bombs to hide their position; it tells the enemy your general location but they can’t shoot you because they can’t see your exact location.
I question this claim, as it was commonplace for prolonged depth charge attacks to occur against subs in WWII (sometimes involving hundreds of such devices; one U-boat survived well over 600 depth charges in a single attack). Subs were often sunk due to cumulative damage from a prolonged depth charge assault, or due to the effect of a single charge finally occurring close enough to the sub to mortally wound it.
If sonar was routinely rendered ineffective for up to 15 minutes owing to a depth charge explosion, it would’ve been far easier for subs to evade and get away.
Note also that so-called “hedgehog” devices deployed a spread of depth charges, so it was less crucial for antisubmarine vessels to precisely locate a sub through sonar.
It was very much an issue limited to the techonology used in WW2, and it was a localised effect in any case.
The issue arose due to two main factors:
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The sonar the Brit’s invented called ASDIC, was an active sonar system, ie it sends out pulses of sound and detects the sound waves that are returned after bouncing off submerged objects. Which includes the highly disturbed water created by a depth charge. It d important to note that the emitter is a single point source on the ship.
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The other factor is throughout WW2 depth charges were simply rolled off the stern of the ship, during which the ship had to be travelling at a certain speed to avoid damaging itself. Thus the explosions were occurring between the ship and the submarine. Through mid to late war depth charge launchers were deployed, but their range wasn’t great, and they made the issue worse really, because they were used in conjunction with the charges rolled off the ship to create a ‘spread’ of depth charges. So now you have a whole line or fan of disturbed water between you and the enemy sub.
There were some workarounds evolved at the time and military technology and doctrine make exploiting it as a tactic of no use. Several issues:
- A tactic used at the time was, where available to have multiple sonars on different ships running to bypass the disturbed water.
- After reaching their ‘peak’ in the 60’s with nuclear versions, depth charges have essentially been removed from the inventory, USN and RN at least no longer even mount depth charges/launchers on their ships.
- Guided torpedoes replaced the depth charge as the anti-submarine weapon of choice. Far more accurate and they can be launched several kilometres away, saying nothing of being able to be dropped by helicopters and aircraft.
- The improvements in passive sonar, which don’t have the same active, bouncing sound wave issues.
I will mention though that the concept was actually used as a decoy by modern submarines for many years, from the 60’s a least I believe. Where a canister was ejected which produced masses of bubble, causing essentially the same water conditions as a depth charge. It was primarily intended to decoy a torpedo, whose active sonar seeker would bounce of the bubbled area, losing it’s contact with the submarine.
- Yeah they bounced active sound pulses off submerged targets and could potentially be confused by the ship’s own depth charge explosions among other things that might reflect sound: sea animals and natural phenomena, also deliberate turbulence stirred up by sharp turns by the sub besides bubbling decoys as have been mentioned. So for all those reasons losing contact on a sub but persisting in the area and regaining it after 15 minutes was no huge setback to effective WWII ASW ships. A key to their success was persistence. Hundreds of subs of all navies escaped attacks where surface ASW forces gave up too soon. Some subs were killed right away by the ships or a/c first detecting them, but many in prolonged hunts where losing and regaining contact after some minutes was an expected part of the process.
The assumption about modern ASW tends to be that it would be ‘one and done’ mainly using guided torpedoes as the final step in the ‘kill chain’. But there’s extremely limited actual combat experience of ASW in the last 70+ yrs. The unsuccessful ASW actions of the RN v the Argentine sub San Luis in the 1982 war (the sub itself also unsuccessful in its attacks) suggest a similar pattern of long and difficult hunts with many torpedoes launches per kill, but even that now is a long time ago.
- Nuclear depth charges have actually been proposed as decoy as well as kill devices. Their explosions were found to ‘blue out’ acoustic sensors for periods of hours rather than minutes over large areas. This was mainly a point of discussion as a problem with their effectiveness in killing subs, if they precluded further attacks or even assessment of the first attack for a long period. But it was mentioned at least sometimes that they might be used as wide area decoys, mainly for surface forces to travel at high speed immune from passive acoustic detection by subs in the area as opposed to subs escaping surface ship attacks.
Use of conventional explosives as decoys would have the disadvantage already mentioned, under the general assumptions of post WWII ASW: that it would signal the direction to the submarine to the passive listening devices now once again important or even dominant in antisubmarine warfare (as passive hydrophones were in late WWI and some navies’ efforts in early-mid WWII). And small explosions would not confuse such sensors with reverberations from every direction the way a nuclear ‘blue out’ might.
WWII subs (at least the German) had a typical max underwater speed of 7 knots (in which they were very noisy and the batteries would drain fast), more often they would operate at 2-3 knots while submerged. You do not get very far at 2 or 3 knots during 10 or 15 minutes, when the hunters can do 30+ knots and use active sonar to relocate you, so getting away was still a challenge.
A sub being hunted by a dedicated hunter-killer team of 3 or more destroyers would be almost surely killed from 1943 onwards, when both tactics and technical improvements had rendered the problem of noise-pollution due to depth charges more or less mute.
My emphasis - nice oops.
Subconscious pun 
The British invented “hedgehog” in WWII which fired a volley of small missiles that exploded on contact with the sub rather than at a determined depth. How effective was it?