Is there a massive underwater blast caused by the implosion of a sinking submarine?

Factual Questions
1

I’m going to try this again. I’m interested in an often reported massive underwater “explosions” sometimes associated with a submarine sinking in WW II. I speculate that this is implosion due to passing beyond the submarine’s maximum pressure depth.

I posted a thread that was too broad on this subject, I think, as one comment noted. Also, the results, in terms of authoritative technical comment, as opposed to interesting speculation, were not conclusive.

It has been suggested in the first thread I posted on this that it might be the submarine intentionally detonating its torpedos as self-destruction. This seems unlikely to me (and to other commenters on the first thread). I’m still interested in this phenomenon, so I’ll try it one more time, more focused.

Here is a long quote from Wikipedia on a series of six submarine sinkings by the U.S. Destroyer Escort “England” in the Pacific in WW II. These were all Japanese submarines sunk within a remarkably short period, and several had in common the massive underwater “explosion” detected by the England, when no anti-submarine ordinance was in the water.

[begin Wiki quote]

"Anti-submarine record

I-16

United States Pacific Fleet Military intelligence decoded a 13 May 1944 message from Japanese submarine I-16 including a scheduled delivery of rice for Japanese troops at Buin on the southern tip of Bougainville Island. England, George (DE-697) and Raby (DE-698) were ordered to intercept I-16. England detected I-16 during calm, sunny weather on the early afternoon of 18 May 1944. The first Hedgehog mortar attack at 1341 was a miss. A second Hedgehog attack scored one hit at a depth of 130 feet (40 m). A third Hedgehog attack at 1410 missed because depth was assumed to be 200 feet (61 m) rather than the 325 feet (99 m) revealed by the fathometer following the attack. I-16 outmaneuvered a fourth Hedgehog attack. The fifth Hedgehog attack at 1433 scored four to six detonations and was followed by a large underwater explosion which lifted England’s fantail and knocked men off their feet. Debris began floating to the surface twenty minutes later. The following day, a three by six-mile (5 by 10-kilometer) oil slick marked the location on the calm surface of the Pacific.

RO-106

A 20 May 1944 message was decoded revealing Japanese plans for a submarine trap north of the Admiralty Islands to intercept an anticipated movement of United States aircraft carriers. RO-104, RO-105, RO-106, RO-108, RO-109, RO-112, and RO-116 of the Japanese seventh submarine squadron formed a patrol line across a route Admiral Halsey had used twice before. George detected RO-106 on radar at 0350 on 22 May, saw the submarine dive when located by searchlight, and missed with a Hedgehog attack at 0415. England regained contact at 0425, missed with one Hedgehog attack, and scored at least three detonations on a second attack at 0501. A large underwater explosion was detected as England prepared to conduct a third attack, and a heavy oil slick with debris was evident after sunrise.

RO-104

The three destroyer escorts formed a search line with a scouting interval of 16,000 yards during hours of darkness. Raby detected RO-104 on radar at 0600 on 23 May, made sonar contact at 0610, and missed with four Hedgehog attacks beginning at 0617. George missed with a Hedgehog attack at 0717. George then missed with four more Hedgehog attacks between 0730 and 0810. England then missed with a first Hedgehog attack and scored an estimated ten or twelve detonations on a second Hedgehog attack at 0834. The hits were followed by noises of the submarine breaking up and a large underwater explosion three minutes later. Debris and oil appeared on the surface at 1045.

RO-116

George detected RO-116 on radar at 0120 24 May. England made sonar contact at 0150, and scored three to five detonations on the first Hedgehog attack at 0214. Breaking-up noises were not followed by the major explosions noted on earlier sinkings. A small quantity of oil and debris was evident after sunrise at 0702 and the oil slick had expanded to cover several square miles the following day.

RO-108

A hunter-killer group consisting of the escort carrier Hoggatt Bay (CVE-75) with destroyers Hazelwood (DD-531), Heermann (DD-532), Hoel (DD-533), and McCord (DD-534) arrived on 26 May so the three destroyer escorts could leave to refuel and rearm. The destroyer escorts maintained their search formation en route to Manus. Raby detected RO-108 on radar at 2303 26 May. England made radar contact at 2304, sonar contact at 2318, and scored four to six detonations with the first Hedgehog attack. There was no major explosion following the breaking-up noises, but a fountain of oil was observed rising to the surface at dawn.

RO-105

The three destroyer escorts reached Manus at 1500 on 27 May. After taking on fuel, provisions, and ammunition, they sailed at 1800 28 May with Spangler (DE-696) to rejoin the search. Hazelwood detected RO-105 on RADAR at 0156 on 30 May and missed with a depth charge attack. George and Raby joined Hazelwood and made sixteen Hedgehog and depth charge attacks over a period of 25 hours. RO-105 came up for air at 0310 on 31 May and was immediately detected by George and Raby. RO-105 stayed directly between the two destroyer escorts for five minutes before submerging so neither Raby nor George could fire without endangering the other. Sequential Hedgehog attacks were then made by Raby, George, Raby, and Spangler. All missed. Division Commander Hains then radioed, “Oh, hell. Go ahead, England.” England then scored six to ten detonations in a Hedgehog attack at 0736. A major explosion followed at 0741 and a fountain of oil and debris appeared on the surface.

This anti-submarine warfare performance was never matched in World War II, and won for England a Presidential Unit Citation, and the assurance from the Chief of Naval Operations, Admiral E. J. King, “There’ll always be an England in the United States Navy.” His pledge was fulfilled on 6 October 1960, when DLG-22 was assigned the name England."

[End Wiki quote]

It is the large underwater explosions, of course, that interest me as possibly caused by imposive force, and I have read of other such “explosions” felt by anti-submarine forces fighting the Germans in the Atlantic. Is this phenomenon due to implosion, or something else? How much force are we talking about if the results are so dramatic on the surface?

2

There’s an oddity in the quoted passage:

Unlike depth charges, Hedgehog bombs were contact weapons. They were fired into the water and sank in a (rough) pattern, exploding on contact. Assuming the wrong depth wouldn’t, in theory, affect a Hedgehog attack because the bombs would just keep sinking and explode deeper down (assuming they contacted the submarine’s hull).

3

Yes it sounds odd, but perhaps there is some technical element missing: like an arming depth set on hedghog “mortar” bombs?

4

Well, in terms of stored energy released I calculate about 1 GJ (or about 0.2 tons TNT equivalent) for full depressurization at 200 m depth for something like a Ro-100 class. The energy released scales linearly with depth, if you prefer a different assumption there.

5

Mis-estimating depth would not affect a Hedgehog attack on a stationary submarine, but it would in the more likely case of a moving one. The time from launch to 200’ depth was around 17 secs, and sink rate around 23.5ft/sec. So the center of a salvo aimed at a 200’ depth sub traveling at 12ft/sec (~7kt’s, just as example) would be centered to lead the sub by around 205’ (slightly> than the sub’s length if a RO-100 class). If the sub was actually at 350’, the aim point would be off by 150/23.5*12=76’. That’s not enough for the ~195’x168’ foot elliptical pattern of bombs to miss if it was right on in all other respects assuming 200’ depth, but there’s a substantial chance the 76’ additional travel during the bombs’ flight could add to other errors and cause a miss.

6

ISTM that as the water rushes in, the air contained in the sub gets compressed and pushes back on the water, providing a spring of sorts that gently decelerates the inrushing water. This is in contrast to a cavitation bubble, which violently slams to zero volume and is responsible for all kinds of interesting effects; that’s when shock waves get created that can shatter crab shells (see “mantis shrimp”) and rapidly erode ship propellers and pump impellers.

In other words, I wouldn’t expect a big “WHAM” as the sub implodes (other than from various parts of the sub suddenly colliding with other parts). Maybe more like a WOOF (or a WHOOSH, but not the kind we amuse ourselves with on this site). IOW, I wouldn’t expect the implosion to generate an acoustic signature that an observer might describe as a “massive underwater explosion” - at least not an observer who has previously heard a genuine underwater massive explosion.

7

On the actual question I still think a case like the I-16’s sinking, an energetic explosion felt to that degree on the ship, would be more likely caused by a munitions detonation on the sub, which a Hedgehog might cause by exploding in direct contact with the torpedo room of the sub. The other references to ‘explosions’ in those reports it seems could be the distinct sound of a sub imploding, but there won’t be strong outgoing shock waves through the water from that, the bubble not as energetic as oscillating one from a munitions explosion, nor necessarily monolithic either, and will take some time to reach the surface. This seemed characteristic of many reports of air bubbles and oil reaching the surface from apparently, as far as the attackers knew, sunken submarines in WWII combat. It didn’t typically seem so powerful or distinct (particularly from depth charge explosions when those weapons were used) as to prevent a lot of uncertainty, or overclaiming in case of navies which didn’t impose conservative standards on assessing attacks on enemy subs (like the Japanese for example).

8

The Russian ‘Kursk’ succumbed to a torpedo-room detonation of torpedoes from a high temperature flash fire, due to dangerous torpedo fuel, faulty maintenance, and handling (if I understand it correctly). The results were spectacular.


So, perhaps a fire could do the same in a Japanese submarine of WW II (note the delay between hedgehog attack and “massive underwater explosion”), but so many of the submarines sunk presented the phenomenon that it seems a lot of chance needs to become involved.

9

Another vote for munitions explosion. The implosion of an unarmed sub would not be nearly that exciting on the surface.

Now we don’t know whether the implosion triggers the munitions or something like an onboard fire triggers the munitions which then bursts the hull and the implosion follows.

10

Maybe they overdid it with the Hedgehog mortars and hit literally every single part of the submarines, including the munitions area, resulting in fantastic explosions.

11

The conspicuous lack of a bow in that photo was not caused by the explosion. The photo shows the wreck after the bow section had been sawn off by the salvage team using a tungsten carbide abrasive cable.

12

Yes, I know that, but I thought the photo gave a sense of the amount of damage. Sounds like you read the same article on this that I did.

There is a graphic drawing of the actual damage at the link above.

13

…and now I’m wondering what would cause a “genuine underwater massive eplosion?”

14

Thanks for this.