Depth charges


Does anyone have any insight into the tactics and applications of depth charges? How well did the concussive shock wave transit through ocean water? I would imagine the energy loss would be rather substantial. How many depth charge rounds are typically deployed in an attack?.. How many hits were required to disable or scuttle a submarine?

Were WW II Japanese Imperial Navy surface ships able to track submarines that had submerged? I was under the impression they were not. The thought occurs to me that were I captain of a submarine under that sort of attack I would order a 90º course correction.

reply

Japanese ASW tactics were not well developed until late in the war when it did them little good.

They quite often underestimated the depth capabilities and as a result, set their DC's too shallow. This was especially true of the later Fleet Type subs like the Gato and Balao class.

The Japanese were very adept at detecting and tracking a sub, but they did not fully prosecute their attacks to the fullest. Often they made several passes, then broke off, leaving the sub to escape. One example that is the exception to their not prosecuting to the fullest but demonstrates their ability was with USS Tang under the command of Dick O'Kane. They were held down for a full day but a PC. Tang's trim pump was causing a little bit of noise from the electric motor and the PC kept tracking it and dropping charges. Tang would shut off the pump and the PC would lose contact, Tang would try to sneak away but soon they had to turn the pump back on to get rid of the accumulated water in the bilges makign her heavier. As soon as the pump came on, the PC would race in with a DC pattern. and the whole cat and mouse would start over.

The Japanese were very inovative as well. Twice Tang was kept down and several targets got past by a Patrol boat using a Depth finder. Tang though it was a sonar. This happened off the coast of Honshu.

Now to Depth Charges.
Water does not compress to any appreciable degree. Thats why when you lower yourself into water, and the water has time to move out of your way, its ok, but do a belly flop and WHAP! it STINGS!

Because of this, shock waves travel VERY WELL through water. much more so than Air. Much more so than the Subs hull itself. Water acts as a solid and transmits the shockwave as a solid. The Energy of the detonation is transmitted to the surrounding water but it attempts to make its escape in the most convenient path. Hence most of the energy is directed straight up. A DC detonating under the boat is more deadly than one exploding over it. This is why both Germany and USA tried developing magnetic exploders and tried to detonate torpedoes UNDER ships rather than hitting the sides.

Air, Steel, wood, lead, all the various things that make up a Submarine, most especially the air, DOES Compress. A DC exploding nearby will seek the easiest way to release that energy of the shockwave. The water won't compress, but that viod of air nearby will. So in a sense, the void of air filling a sub, acts as a magnet to draw the force of the explosion to it.

As to patterns and how many...
That depends on the Ship in question and what it's DC capability is. How many racks, how many K-guns etc... How many reloads does it have?

Typically though on a well armed destroyer with plenty of reloads...
The DD would charge straight toward the sonar target that is the Sub.
the Captain would make a judgement as to when to drop. and two would roll off the stern racks, followed a few moments later by the Port and starboard K-Guns which would throw charges off to the side, followed by a couple more off the stern racks. If there are more than two K-guns per side, they could vary the depth settings to cover a greater spread. Also the second set of stern charges would be set deeper as the sub would be seeking depth to escape.

This is all to create a pattern that hopefully would land a few charges close enough to destroy the Sub. Often it took multiple passes before a hit was assured, unless the sub was caught at periscope depth and the DD had a good idea of depth setting to use.

Depth was the ally of a Submarine. in WW2 the depth of a sonar contact was as much an educated guess than anything else. DC's had to be pretty close to do any good. the greater the depth, the longer it took for the Charge to sink to that depth, the greater the time the sub had for evasion. This is not without it's drawback however. Any DC that DOES come close enough at depth, is more likely to destroy the sub as opposed to one that is shallow, because of the greater sea pressure acting on the hull already.

Late in the war, the US and other allies started using teardrop shaped charges rather than the Ashcans typical for most of the war. These streamlined charges dropped much faster and negated a lot of the advantage a sub had in seeking deeper depths. I dont remember the name of the ship, Started with an R I think, but it was assigned to the Eastern Sea Frontier off the US East Coast. they were testing the new Teardrop charges and their first try was at slow speed in shallow water. Needless to say, the charge went off far faster than they expected and the Destroyer was not too far away when it happened. the Shock was transmitted right into the stern of the ship and damn near sunk her. It blew all the power and knocked her engines off their mountings.

If a DD is about to sink. it was very important for one of the crew to safe the DC's before abandoning ship. Many a whole crew has been whiped out by their own ships charges going off underneath them. The Shock wave would quite literally Split open their ribcages.

Even at a distance, the charges were dangerous to anyone in the water. Hence the term "Salt water Enema", many sailors had for them. The shock wave even at a distance, had the power to force seawater past an oriface like your sphincture muscle.

And on that note... I think I'll close this post




I joined the Navy to see the world, only to discover the world is 2/3 water!

reply

Thank you for such a comprehensive reply!

reply

For a lot of insight into action on subs in the Pacific, read "A Tale of Two Subs". The Japanese navy did eventually have sonar. The closer the depth charges were to the sub, the worse it was. If they exploded VERY close, they produced an effect called cavitation, which could be catastrophic to a submarine, causing it to literally blow apart. This same effect is used with modern-day torpedoes, which are designed to explode just below the keel of ships. The cavitation causes the keel to literally shatter, breaking the ship--the ensuing explosion and force of water then goes right into the now-open hull and blows the ship apart instantly. Very devastating, very quickly.

There was a nasty occurrence during WW II when a nitwit politician was mouthing off to the press about how well things were going in the Pacific war, and particularly about submarines. He foolishly commented that the Japs were setting their depth carges too shallow anyway. After that, a lot of American sailors died on submarines when the Japanese began setting their depth charges a lot deeper.

This guy should have been executed for treason.

reply

Overall a good post but for your comments about cavitation being the physical property that causes the damage from depth charges.

Cavitation is to be avoided for several reasons, one of them being damage. But not from depth charges.

Cavitation is an area of low pressure created behind a moving object that creates a vacuum bubble in water that instantly collapses. For example the trailing edge of a quickly rotating propellor blade.
http://www.youtube.com/watch?v=GpklBS3s7iU

Not only is it very noisy and can alert the enemy as to your position, but the collapsing bubbles impacting upon the blade can pit and erode the blades.
http://www.originalpropshop.com.au/Images/800px-Cavitation_Propeller_D amage.jpg

Damage from a depth charge has nothing to do with cavitation.
It has to do with the unceompressability of water and the shockwave that results from it.
Water does not compress to any appreciable degree and therefore when a detonation takes place, the shockwave needs to expend its energy somehow. It does this into the nearest compressable object (Usually AIR). Normally the nearest air is straight up to the surface and thus you get that common shot of the water surface jumping then exploding upward in a pillar of whitewater.
When a Submarine is nearby. it is easier for the shockwave to expend its energy by compressing the air inside the sub. The water between the explosion and the hull offering less resistance than all the water above the eplosion and the surface.





I joined the Navy to see the world, only to discover the world is 2/3 water!

reply

Depth charges rely for their destructive power on a reentrant jet directed toward the submarine upon the collapse of the explosively generated bubble in the vicinity of the solid outer surface of the target submarine. The bubble is a consequence of cavitation resulting from the detonation of the depth charge, the type of cavitation that results from movement of the liquid, not an object through a liquid. The shock wave has a role to play as well, but it is the effect of the collapsing bubble that contributes most to the destructiveness to submarine hulls, causing highly localized & transient surface stresses. Repetition of these stresses by sustained depth charge attack can eventually cause catastrophic structural failure.



And I can't believe there is THIS kind of exchange going on on a movie message board!

reply

And I can't believe there is THIS kind of exchange going on on a movie message board!


LMAO!

You should look up the thread concerning Submarine operating procedures and the long arguments over just what property of physics is responsible for bouyancy and how a Sub maintains its bouyancy.

After an exhaustive argument about what actually bouyancy is and is not and in cases quoting directly from US Navy official manuals, there were still idiots insisting that bouyancy was due to density. They argued that you change the density of the sub to make it rise or sink. Density has nothing to do with bouyancy other than in an incidental and indirect fashion.
You don't change the density of the sub, you change the amount of water displaced by the sub.


Also I guess you must be new because these "movie" message boards are not exclusive to talking ONLY about a specific movie. Often people who are regulars here come on here to discuss the topics the movie is about, not the movie itself.

Wanna discuss WW2 in Europe? Go the the "Saving Pvt Ryan" message board.

Wanna talk consiracy theories? Go to the "United 93" or "World Trade Center" boards.

Wanna talk NASA and the space program? got to the "Apollo 13" boards.

Wanna talk about Subs? Go to "Das Boot","Run Silent Run Deep","Red October","Crimson Tide", "Down Periscope", or any other number of boards.

Technical details of US Depth Charges of WW2.
http://www.hnsa.org/doc/depthcharge6/index.htm


And so sorry but you are wrong in your post.
Just like the guys that kept arguing that it is DENSITY that you must change, you get the principle right but you misread the cause.

You are right when you talk of a reintrant jet, etc.. but wrong in calling it cavitation. It is the collapse of the bubble and the re-intrant jet as you call it that causes the damage but cavitation has nothing to do with it.

Underwater detonations SUPERFICIALLY resemble cavitation bubbles when the bubble created collapses. But they are NOT the same thing.

Cavitation bubbles form because of a region of low pressure creates a vacuum bubble which then collapses when the bubble moves out of the low pressure region.

The bubble from an explosive blast forms because of the high pressure shockwave, then collapse as the pressure moves outwards leaving the low pressure bubble behind.

The effects of underwater explosions, such as that generated by torpedoes or mines, are much more devastating than a similar explosion in air. Over the last decade a numerical code on underwater explosion and bubble dynamics has been jointly developed by faculties at the Department of Mechanical Engineering, NUS, and researchers from the Institute of High Performance Computing (IHPC), to understand better the underwater explosion phenomenon and its devastating effects.

Figure 1 gives an example of the detailed results of our simulation run. Figure 1(a)shows an explosion which takes place near a flat vertical immobile solid plate. A bubble forms at the epicentre of the explosion (Figure 1(b)which grows very rapidly to its maximum volume. It then collapses rapidly while moving towards the plate. At the same time, a high-speed jet is formed, propagating though the collapsing bubble. A very high pressure is generated on the plate as the jet impacts on the other side of the bubble, while the bubble continues to contract until it reaches its minimum volume. In Figure 1(j),the bubble starts re-expanding again and the process repeats itself despite the much lower expansion and implosion energies.

The potential devastating effect of an underwater explosion on a ship is shown in Figure 2.At the moment of explosion, a shock wave propagates through the water (in a few milliseconds). This shock wave will have a first damaging impact on the ship body (Figure 2(a)).This figure also shows the creation of a bubble at the epicentre of the explosion. The high pressure gas bubble expands very rapidly. At the same time, the ship will bend upwards and its hull is weakened (Figure 2(b)).After reaching its maximum volume, the bubble collapses eventually due to the effect of inertia. The pressure will now be lower than the surrounding reference pressure, causing the ship body to bend downwards (Figure 2(c)).During this collapse phase the bubble is attracted to the ship body. In the final phase of the collapse, a high-speed jet is formed. This high-speed jet can easily cut through the ship body. This mechanism has been identified as being a second cause of damage (and probably even the most devastating one) that appears during an underwater explosion (Figure 2(d)).After the bubble has reached its second minimum a similar cycle can begin. However, as the bubble has lost much of its energy, the following oscillations will not have as great destructive power in general.

Some small-scale experiments have been carried out and were compared successfully with the obtained numerical results like in Figure 1.The validated code can be applied to other relevant engineering problems, for example, in cavitation on ship propellers (where tiny vapour bubbles can cause a lot of damage on these propellers) or in medical applications. The method of imploding micro-bubbles with ultrasound in biological flows to remove kidney stone or growth is also based
on the same physics, but on a much smaller scale of course. This research is carried out in collaboration with Assoc Prof Yeo Khoon Seng of ME Department and IHPC (Institute of High Performance Computing).

http://www.eng.nus.edu.sg/EResnews/0306/rd/rd_12.html

And here is a popular video demonstrating the effect on a surface vessel just as is shown in figure 2.
http://www.youtube.com/watch?v=RV8MF-440xg

and here is aillustration of the effect against a Submarine as in thwe case of Depth Charges.
http://www.fas.org/man/dod-101/navy/docs/es310/uw_wpns/IMG00003.GIF


I joined the Navy to see the world, only to discover the world is 2/3 water!

reply

"There was a nasty occurrence during WW II when a nitwit politician was mouthing off to the press about how well things were going in the Pacific war, and particularly about submarines."

Who was the politician?

reply

Early in the war, The Japanese did not know just how deep our subs were capable of and as a consequence, they always set their DC's too shallow. We knew they were being set too shallow and exploited it by always going deep and the Japanese could not hit us.

The House Military Affairs Committee had visited the pacific theater and was given several briefs. This information was part of one of the briefs.

One member was Congressman Andrew J. May. This jacka$$ goes and holds a press conference and to show how well informed he is, he reveals to the press that the Japanese are setting their charges too shallow.

this is picked up by the wire services and soon newspapers all over are reporting this story.
Shortly thereafter the Japanese redesigned their exploders to go off deeper.

A very pissed of Admiral Lockwood (COMSUBPAC) wrote a scathing letter to the congressman and told him to be rest assured that the Japanese are now setting their depth charges to the proper depth.

Lockwood estimates that at least 10 subs and 800 submariners were lost direrctly because of this A-hole.

Loose Lips Sink Ships!

This A-hole also used his congressional position on the Military Affairs Committee to accept bribes for favorable munitions contracts. He was convicted of war profiteering and served 9 months in federal prison until he recieved a pardon.




I joined the Navy to see the world, only to discover the world is 2/3 water!

reply

And don’t forget the Garsson munitions case.

Andrew Jackson May (D), a member of United States House of Representatives from Kentucky was known to telephone army ordnance and other government officials to award war contracts, obtain draft deferments, and secure other favors for friends such as Murray Garsson and Henry Garsson, two New York businessmen who had no prior arms manufacturing experience yet had obtained lucrative munitions contracts from the U.S. Government.

After WWII, a Senate investigating committee reviewing the munitions business discovered evidence that May had received substantial cash payments and other inducements from the Garrsons. The review revealed that the Garsson factory produced 4.2-inch mortar shells with defective fuses, resulting in premature detonation and the deaths of 38 American soldiers.

May was convicted by a federal jury on July 3, 1947 on charges of accepting bribes to use his position as Chairman of the Military Affairs Committee to secure munitions contracts during the Second World War, and served nine months in federal prison. However, President Truman (D) decided to grant May a full pardon in 1952, and he continued to retain influence in Democratic party politics.

Sound familar? Looks like “Pay To Play” was in full effect even back then.

reply

Yup. And that is why I am so virulently anti-Hillary.

I joined the Navy to see the world, only to discover the world is 2/3 water!

reply

And speaking of the devil... you may not believe this but her motorcade passed right by me about 1/2 hour ago on Sunrise Blvd down here in Fort Lauderdale. I have never seen so many police motorcycles, sheriffs, highway patrol, and state troopers in my life!

Apparently she's here stumping in our sunny "hanging chad" swing state. Already a lawsuit has been filed in my county (Broward) because of problems with early voting.

reply

Lol. Speaking of hanging chads and Broward county...

Back during that fiasco, I was in a chat with some friends and one girl was from Japan, and another friend was from Broward County.

My Japanese friend gave her opinion on the situation which my other friend didn't care for so he responded with, "You're not American. You're from Japan, so your opinion doesn't count."

I rwponded back," Look who's talking, you're from Florida. You can't count!"

lol

I joined the Navy to see the world, only to discover the world is 2/3 water!

reply

I see you were on the USS Halsey. She still had Terriers right?

My brother was on the USS Boston (CA-69/CAG-1), a WWII heavy cruiser that was refitted to become the first guided missile cruiser. He said when they first got and tested them, all aboard took cover because the Terriers had a tendency to turn and come back!

reply

CGSailor,
As a former US Navy Sonarman (USS King DLG-10) and friends with a number of submariners, I found your posting wonderfully informative and I have to believe you answered all questions. Well done sir.
pjaudinetsr

reply

Thank you.

My first ship too was originally a DLG though I was aboard after the hull realignment program of the 70s-80s Afterwards we were known as CG's
CG-16 Leahy class (originally DLG-16)

I served on CG-23, USS Halsey.


I joined the Navy to see the world, only to discover the world is 2/3 water!

reply

I'm not an expert, but to give a straight answer to your question I think with WWII subs and DCs an explosion within 200 feet would buckle plate. Closer and serious damage results.

reply

I just read up and the U.S. depth charges were a little puny but at 20 feet a hull rupture would result. Most of the time subs were damaged from repeated near hits rather than a single hit close in.

reply

The truth is that there were several DC explosions in that movie that should have had the Nerka's number. Like that one that bounced off the diving plane and blew up about six feet later.

When a loose cannon flogs a dead horse, there's the Devil to pay!

reply

@fskpilot: I agree with your observation about several of the DCs exploding at point-blank range with only minimal sub damage occurring.

However, I don't know if the special-effects personnel were able to detonate each DC with an individual transmitter/ remote-control while watching alongside the film camera or had to rely on a timer and therefore be at the mercy of local water currents flowing around the sub ultimately determining the rate of fall and its path.

BTW, the latter would require a supercomputer to solve multiple equations describing the chaotic motion of the local water currents - assuming that said eq'ns even exist....

reply

They also used "hedgehogs" that were 24 14.5kg mortars, fired in an S pattern, that would explode upon contact w/the submarine. So these could be quite devastating because of their close proximity upon exploding, and they didn't depend upon getting the depth correct.

reply

[deleted]

They also used "hedgehogs" that were 24 14.5kg mortars, fired in an S pattern, that would explode upon contact w/the submarine. So these could be quite devastating because of their close proximity upon exploding, and they didn't depend upon getting the depth correct.


There was also "Squid" which was a three barrelled mortar that fired tear drop shaped charges ahead of the ship. They were usually used in pairs (i.e. 6 barrels) and were associated with a depth finding sonar and ranging sonar. The sonars fed into an analogue computer which was connected to a fuze setter (the charges had time fuzes like AA shells). The ranging sonar gave the slant range and bearing which, together with the depth, could be used to calculate the position of the sub. At the right moment, the 6 barrels were fired automatically. The Squid had about a 40-50% success rate, which was much better than depth charges.

From aircraft, there was the Mk 24 "mine" ("FIDO"), which was an acoustic torpedo. It was carried by Liberators and was supposed to be dropped into the wake of the sub as it submerged. It also had a much better success rate than depth charges.

reply