Monday, November 27, 2017

Torpedo and Mine Damage History - Part 1

We previously examined torpedoes and their lethality and debunked the “broken back over a bubble of air” myth by examining available experimental data and applying simple logic (see, "Torpedo Lethality Myth").  However, it’s always worth looking at actual operational experience so let’s look at some historical examples of ships subjected to large underwater explosions due to mines and torpedoes and see what we can learn. 

This is the first of a two part post.  In this part, we’ll look at the historical data.  In the second part, we’ll examine an explanation for the historical data.

I’ve tried to pick a cross section of ship types, sizes, eras, and nationalities while working under the constraint of known data.  Many ships suffered mine/torpedo damage but the damage was too poorly documented to analyze.  The following examples are presented in no particular order.



Tirpitz

Tirpitz is one of the most documented and relevant examples.  According to Wiki, X-Craft midget submarines laid four 2 tonne mines on the sea bed under the bottom of the target.

“first exploded abreast of turret Caesar”

“second detonated 45 to 55 m (148 to 180 ft) off the port bow”

A fuel oil tank was ruptured, shell plating was torn, a large indentation was formed in the bottom of the ship, and bulkheads in the double bottom buckled. Some 1,430 t (1,410 long tons) of water flooded the ship in fuel tanks and void spaces in the double bottom of the port side, which caused a list of one to two degrees, which was balanced by counter-flooding on the starboard side. “

The mines were massive explosions and caused extensive damage but no threat of sinking and no significant permanent structural damage.  In fact, the damage was repaired over the course of a few months.  These mines probably represented a worst case under-the-hull explosion of the type we’re interested in.

In a later attack, RAF Lancaster bombers attacked with 6-short-ton Tallboy bombs with 5200 lb Torpex D1 explosive.  A single hit on the ship's bow penetrated the ship, passed through the keel and exploded on the bottom of the fjord.  A thousand tons of water flooded the bow and caused a serious increase in trim forward but the ship did not sink.

Along with many bomb hits distributed over several aerial attacks which eventually sank the ship, Tirpitz absorbed three massive underwater explosions of the type we’re concerned with.  In fact, the explosions were probably much more powerful than a torpedo and yet they failed to inflict significant structural damage.

Prince of Wales / Repulse

PoW
-          torpedo hit on outer port propeller shaft exit causing extensive flooding and an 11 degree list to port
-          torpedo hit starboard bow
-          torpedo hit starboard alongside B turret
-          torpedo hit starboard alongside Y turret

Repulse
-          Four or more torpedo hits

Note that Repulse lacked anti-torpedo blisters and modern internal compartmentation.


Yamato

The Japanese battleship Yamato was subjected to multiple waves of attack.

First wave:

-          torpedo hit port side, forward which caused little damage
-          two torpedo hits port side near engine and boiler rooms
-          probably torpedo hit near auxiliary steering

Hits cause an initial list which was corrected with counterflooding.  Top speed was only slightly affected.

Second wave:

-          three or four torpedoes hit port side and one to starboard

This attack caused additional listing but did not put the ship at risk of sinking.

Third wave:

-          Three torpedo hits port side concentrated along the engineering spaces
-          Torpedo hit starboard

At this point, the ship began to sink.  In addition to the numerous torpedo hits, many bomb hits caused additional damage.


Musashi

Musashi was a Yamato class battleship that was sunk on 24-Oct-1944.  The ship suffered numerous bomb hits and the following torpedo hits.

-          1 torpedo starboard amidships which caused some flooding
-          3 torpedoes port side
-          4 torpedoes, three of which hit the forward bow
-          3 torpedoes starboard bow
-          11 torpedoes various locations

The ship sank intact.


Belgrano (Brooklyn class light cruiser)

The Argentinean cruiser was a 44 year old pre-WWII ship, poorly maintained, served by an ill-trained crew, and sailing with all watertight doors open when it was hit by three British 21” torpedoes.  The first exploded just forward of the armor belt and damaged the bow but did not threaten the ship’s stability.  The second hit just aft of the armor belt and opened a large hole which caused severe flooding.  Reports suggest that the third torpedo hit but it is uncertain whether it exploded.

None of the torpedoes broke the ship’s back and the first didn’t even hazard the ship.  The second caused flooding beyond the ill-trained crew’s ability to handle and led to the ship sinking.  It is likely that a well maintained ship, sailing at combat readiness (watertight doors closed), and with a trained crew would have been able to contain the damage and save the ship.


Bismarck

Prior to the action that directly resulted in the sinking of the Bismarck, the ship had suffered shellfire damage though the damage appeared to have no direct impact on the ship’s survivability.

On the evening of 24-May-1941, Bismarck suffered a single torpedo hit which caused only superficial damage to her armored belt.  Other reports suggest several torpedoes hit but did no significant damage. (1)

On the evening of 26-May a torpedo struck Bismarck’s port side and jammed her rudder.

On 27-May, British battleships and cruisers eventually wrecked Bismarck’s upper decks with the Bismarck absorbing as many as 500 shell hits. (1)  Torpedoes were launched by the British ships but the number of hits, if any, are unknown.  Two possible hits were reported. (2) 

Dorsetshire fired two 21 inch torpedoes and both hit the starboard side with no appreciable effect observed.  Another torpedo struck the port side, again with no visible effect.

Bismarck settled deeper into the sea and eventually capsized and sank.

In all, Bismarck suffered at least 5 confirmed torpedo hits and possibly 7 or more.  Other than to contribute to the cumulative flooding, the torpedoes caused no catastrophic structural damage.


HMS Belfast (light cruiser)

The cruiser Belfast struck a magnetic mine in November of 1939.  The ship suffered moderate damage and was repaired and returned to service.  Belfast was 613 ft long and around 11,000 tons displacement.

Photos of the ship in drydock suggest that the mine exploded under the hull, slightly offset to one side.  The explosion caused little direct damage to the hull, leaving a small hole, but did cause shock damage and warping of decks and structural members.  The keel was bent upwards by three inches.

The ship was, apparently, in no danger of sinking at any time.

This was a nearly classic example of the torpedo/mine exploding under directly under the hull and should have been a perfect example of the “broken back due to  suspension of the ship over a bubble” if the phenomenon were true.



Lexington (CV-2)

Two torpedoes hit the carrier on the port side but the ship was able to continue flight operations until a series of massive gasoline-sparked explosions occurred which eventually led to the ship being abandoned.  A US destroyer was ordered to sink the carrier and fired five torpedoes at which point the carrier settled into the sea on an even keel.


Princeton (CG-59)

During Desert Storm, Princeton suffered two bottom-moored influence mine explosions, one under the port rudder and the other under the starboard bow.  The explosions caused superstructure cracks and hull deformations along with various piping damage, shaft damage, and rudder damage but the ship’s weapons were back on line in 15 minutes.  The ship was able to leave the minefield under her own power.

Again, this was a near perfect example of the “explosion under the hull” and yet they did not break the ship’s back nor threaten the ship’s survival.  Further, this is a case of an explosion occurring under a modern, weakly built (as compared to a WWII ship of similar size) hull and yet still did not sink the ship.


Tripoli (LPH-10)

During Desert Storm, Tripoli suffered a mine explosion from a sub-surface moored mine which caused a 16x25 ft hole in the hull below the waterline.  The ship continued operations after damage control measures.

Again, this is a near perfect example of the underwater explosion effect and the results were negligible as regards ship survivability or even mission effectiveness.

Tripoli Mine Damage


Samuel B. Roberts (Perry class FFG)

A mine explosion blew a 15 ft hole in the ship and broke the keel triggering flooding and fires on multiple decks.  The mine is believed to have exploded in contact with the ship’s hull.  The explosion occurred on the port side at the forward end of the hangar.  Despite the near fatal damage, the ship was able to maneuver using thrusters at 5 kts and her combat systems and weapons remained operational.  The ship was saved, repaired, and returned to service.  Repairs took 6 months and cost $89M.

This explosion took place a bit to the side as opposed to directly under the ship and came as close to sinking the ship as any of the examples.  This is also the smallest ship in the examples and a modern, weakly built ship.  Despite this, the explosion did not break the ship in two.


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The observation that leaps out from an examination of the historical data is that no large ship has ever had its back broken by a mine or torpedo in the popular “suspended over a bubble of air” scenario.  Yes, a sufficiently large number of mines/torpedoes can cause enough cumulative damage (usually cumulative flooding) to eventually sink a large ship but none has ever been broken and sunk with a single mine/torpedo shot which is the commonly cited claim by the “torpedoes are invincible” crowd.  In fact, not only has no large ship ever been sunk by a single torpedo/mine hit but most have absorbed at least several such hits prior to sinking along with, in most cases, many aerial bombs which contributed to the sinkings.

It is also notable and, frankly, a bit surprising, that even smaller ships have been able to absorb surprising amounts of underwater explosion damage.  The 450 ft long, 4200 ton displacement Samuel B. Roberts was an example of such.

It must be noted that WWII torpedoes were not designed as under-the-keel weapons.  Most WWII torpedo hits impacted the side of the target’s hull somewhere in the lower half of the underwater hull depending on the depth setting of the torpedo and the draft of the target’s hull.  As such, these are not direct representatives of a perfectly placed under-the-keel explosion but they are informative data points, nonetheless.

There is also a school of thought that WWII weapons were not as powerful as today’s.  This is nonsense, as least as far as torpedoes and mines are concerned.  Supersonic, heavyweight anti-ship missiles are another issue but that’s a topic for another time.  Mines haven’t appreciably changed in terms of their explosive power.  Yes, fusing mechanisms have gotten more sophisticated but the raw explosive firepower has not.  The same holds true for torpedoes.  For example, the standard US torpedo of WWII was the Mk14 with a warhead weight of 643 lb.  The current standard US torpedo, the Mk48 has a 650 lb warhead.  They’re identical.

We previously disproved the commonly held belief that torpedoes kill by suspending a ship over a bubble of air and breaking its back.  The empirical evidence in this post further proves that the belief is a myth.  In fact, the empirical evidence suggests that ships can absorb far more underwater explosive effects than anticipated and that even destroyer and frigate size ships are capable of absorbing tremendous damage without structurally collapsing and sinking.

This post should not be read as a claim that torpedoes are insignificant - far from it.  They are powerful and damaging.  The smaller the ship, the more damage an underwater explosion will inflict – no great surprise – and, for smaller ships, such damage may well be fatal.  Still, all ships seem to show a surprising inherent resistance to underwater explosions. 

In part 2 of this post, we’ll examine one of the main, but generally unrecognized, factors behind this resistance to underwater explosions.



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18 comments:

  1. Excerpt from Scott C. Truver, Ph.D. for CIMSEC Next War Blog article on December 20 2016 - NAVAL MINES AND MINING: INNOVATING IN THE FACE OF BENIGN NEGLECT -

    "...it usually comes as a surprise to learn that of the 19 U.S. Navy ships that have been seriously damaged or sunk by enemy action since the end of World War II, 15 – nearly 80 percent – were mine victims.

    This vulnerability to mines has catalyzed the U.S. Navy to spend many hundreds of millions of dollars to counter a global threat that includes more than a million sea mines of more than 300 types in the inventories of more than 50 navies worldwide, not counting underwater IEDs that can be fashioned from virtually any container. More than 30 countries produce and more than 20 countries export mines. World-War I-era contact weapons bristling with “horns” can be as dangerous as highly sophisticated, computer-programmable, multi-influence mines that fire from the magnetic, acoustic, seismic, and pressure signatures of their victims. Ask Captain Paul Rinn, commanding officer of the frigate USS Samuel B. Roberts, how a mine designed in 1908 can ruin your day.

    Of particular concern are the mining capabilities of potential adversaries:

    • Russia reportedly has about a quarter-million mines
    • China, 80,000 to 100,000 mines
    • North Korea, perhaps 50,000 mines
    • Iran, 3,000 to 6,000 mines

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  2. Can anyone speak to how SINKEX ships are usually configured? Are they watertight? I would assume so in order to preserve their capacity as a target.

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    1. That's a great question and I've been unable to get a definitive answer over the years. In fact, I've read accounts that suggest both conditions: readied to sink easily and in a controlled manner and buttoned up to try to resist sinking. I suspect that both are true, depending on the circumstances of the exercise.

      The SinkEx conditions are either classified or not for public consumption as I've never come across a detailed description of an exercise.

      Maybe someone out there has taken part in a SinkEx and can shed some light on it?

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    2. The ships used in a SinkEx are carefully prepared so as not to present an environmental hazard in its final resting place. This means removing all fuel and other hazardous materials. The type of materials that might result in secondary explosions following a strike by a torpedo or missile.

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    3. SINKEX ships are usually watertight at the hull skin, but then the damage control mechanisms that would normally work to minimise flooding have been bypassed or just left open to facilitate sinking. This can be by just making a couple of small holes in key bulkhead places to ensure that the ship will slowly flood in a controlled way.

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  3. Giving more detail about the mining of the Belfast
    "There were nineteen casualties with broken bones-mostly legs-due to the violent whipping caused by the explosion. The direct damage was not unduly severe, centring on the starboard side of the forward boiler room where the outer bottom was badly dished over a length of 20ft, but the effects of whipping were far more serious. Towards the ends of the ship, heavy weights were thrown up with such violence that they hit the deck above. 17 The outer bottom failed in compression, the flat keel being fractured. There was a severe buckle, 14in deep, in the upper deck and there were several fractured plates in the deck. Altogether the ship was bent upwards by some 4ft 6in. This was, in part, due to a failing in structural design which led to problems in Edinburgh and some of the Southamptons. 18 There was a break of forecastle amidships and, nearby, the armour deck and side armour stepped down a deck."

    Brown, D. K.. Nelson to Vanguard: Warship Design and Development 1923–1945 (Chatham's Distinguished Design) (Kindle Locations 5568-5575). Naval Institute Press. Kindle Edition.

    As you pointed out the direct local damage wasnt especially severe.
    Damage to the machinery was even more serious.

    "The cast iron discharge pipes of all the fuel pumps were shattered, oil was spurting out and it was fortunate that there was no fire. The stools of all the turbines in the forward engine room were destroyed as was at least one in the after space."

    Brown, D. K.. Nelson to Vanguard: Warship Design and Development 1923–1945 (Chatham's Distinguished Design) (Kindle Locations 5580-5582). Naval Institute Press. Kindle Edition.

    But 'bent upwards by 4 ft 6 in doesnt sound good and a larger area of structural failure while not dramatic means reconstruction was necessary including longitudinal bulges which meant her stability was improved enough for later modifications to allow her to be the 'last British all gun cruiser'

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    1. "a larger area of structural failure while not dramatic means reconstruction was necessary"

      Hey, no one said ships could laugh at torpedoes and mines, only that a single torpedo is not instantly fatal as the torpedo crowd used to claim.

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    2. Yes. Brown recounted torpedo hits on US warships.
      "A BuShips paper summarised the results of torpedo hits: Torpedoed 31 Of which sunk 7 Hit in machinery 11 Immobilised 2"
      And those were with the massive Japanese torpedoes. Against merchant ships it was a completely different story

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    3. The numbers support your proposition of the lethalty myth

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  4. I've always wondered about the "back-breaker" myth. The multiple ships breaking in halve that have been reported, were they the result of the actual explosion, or the very act of sinking? (i.e. like the titanic, where the weight of the flooded compartments caused the breaking.)

    My apologies in advance if my speculation is misplaced or naïve.

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    1. Between what I've described in the posts and your own observation, you've pretty well answered your own question. Ships that actually break are either small or are showing the effects of multiple hits and cumulative damage. Remember that the premise is that no larger ship has ever suffered the broken back myth from a single torpedo/mine hit. There are ships that have broken after suffering many hits or, as you point out, cumulative damage and flooding but that's not what the premise addresses.

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  5. You might want to consider the fusing mechanism in your analysis.

    The vast majority of torpedo hits (including Long Lance et al) up to and including WW2 were what are known as contact-fused. In other words the weapon ran shallow enough that it detonated when it contacted the hull and therefore there was no "stand-off". The last combat sinking by torpedo (the Belgrano) also used contact fusing, largely because the reliability of the Mk24 Tigerfish at the time was suspect.

    However, the vast majority of modern ASuW torpedoes use influence fusing, precisely to induce "stand-off". The actual mechanism of damage for stand-off undex is complex and not to be discussed on open forum. However, it's fair to say that you usually end up with plastic failure induced by resonance of the hull girder from the oscillation of the bubble.

    One other thing. Don't misconstrue the contribution of the armour belt to longitudinal strength. That's not what it's there for, how it was configured or how it worked.

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    1. "The actual mechanism of damage for stand-off undex is complex and not to be discussed on open forum."

      We've already discussed it at length in the original torpedo myth post. We also noted the change in fuzing from WWII to today. You need to reread and catch up!

      I'll address armor belts as they relate to torpedo resistance in the next post.

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  6. A friend of mine (pun) was assigned to the Tripoli as a chief machinist mate to work on the damage repair. That could be him on the left side photo in the article (tall man in khaki uniform with five sailors in dungarees). He wasn't there when the mine exploded, but he was there through the repairs and would have have extensive knowledge of the damage done. I can pass along any questions you may have for him.

    Thanks for the excellent article; hard to dispute documented historical facts.

    MM-13B

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    1. My main question is how far away from the hull did the explosion occur?

      My secondary question is were any main longitudinal structural elements damaged and, if so, to what extent?

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    2. Spoke to him a couple times over the weekend. Just of the top of his head: explosion was about ten to fifteen feet away from the hull, and no main longitudinal structures damaged. Proper material conditions were set (doors, hatches, and other fitting closed) which contained the damage to a small part of the ship. He has his written notes stashed away, but that is what he remembers. And that is not him in the photo.

      MM-13B

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    3. Well, that supports the overarching theme of these recent posts. Thanks for looking into that.

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