I’m reading Ian Toll’s “Pacific Crucible,” and his description of a massive underwater explosion from a sinking Japanese carrier at Midway is the occasion for a question I’ve had for some time.
What is the nature and power of implosion on a ship sinking into abyssal depths?
In accounts of wartime ships sinking in deep water there are repeated anecdotes of a massive underwater explosion some time after the ship has disappeared. This seems to apply mostly to warships, submarines particularly but also other warship types. Typical descriptions are of such a jarring blast that it seems impossible on the surface, both in sound quality and the force felt underfoot. The power of these blasts make a deep impression on those experiencing them, which is why you read of them often.
I conclude that these are implosions of watertight compartments under the incredible pressures of the sea at depth (and some authors say this specifically). It is the watertight integrity of warships and submarines that set up these blasts, I gather, while commercial ships are likely to fail earlier.
What I’m interested in knowing is the nature of implosion vs. explosion; the power of the forces involved compared to explosive forces; and exactly what happens to the compartment, the air in the compartment (which is not compressible – right?); the ship itself, and anyone unfortunate enough to be still in the compartment when it implodes.
There must be a submariner, a physicist, or a hydrologist out there somewhere who can shed some technical light on this.
I note I made an error in saying air was not compressible. SCUBA divers and physicists might disagree with me on this.
It is water that is not compressible. I was thinking of a scene in the movie “The Score” in which a master burglar (Robert De Niro) breaks into a safe at the Canadian customs house in Montreal by burning a 2+ inch hole in the top (approx.), then filling the safe with water and lowering a small explosive charge (a cylinder about 2"x 6") into the center of the water-willed safe and detonating it. The water, not being compressible, then forced open the safe in response to this small but potent charge.
I’ve heard stories about destroyers getting sunk during WW2. Supposedly, it was common for the depth charges to explode after the ship went down. This often killed the sailors on the surface who survived the inital sinking.
The projectiles would not blow up. They are subject to many times the pressure of a deep ocean when fired from their gun or howitzer and still make it to the target.
“Blind Man’s Bluff” details the end of a number of submarines. The sound/implosion is a result of the collapsing watertight bulkheads.
Not generally, but some are designed to do just that - for example, destroyers have depth charges, which are triggered by pressure. I dunno what safety features they had, but I’ve heard that depth charges going off when destroyers sank was a serious menace to survivors.
Depth charges not yet deployed could set off other munitions.
Another possible factor could be explosions from live steam suddenly cooled, setting off munitions.
…and having worked in a cannery at one point, I can tell you that live steam in a pressure vessel suddenly cooled (as with a water spray at the end of a cook) creates a vacuum in that vessel, requiring compressed air to balance it off and avoid damage to the cans.
A load of depth charges going off at their set depth (not having been properly set to “safe” before the sinking, as happened all too often in the sudden events of war), could be quite dramatic, but it was at fairly shallow depth, while the type of blast I’m addressing here is generally reported at depth, some time after the disappearance of the sinking ship, and thus a surprise to surface observers.
I emphasize that the effects on the surface of whatever is happening is quite dynamic and frightening, felt through the entire ship and even at considerable distance away.
Why would depth charges be going off be at a “fairly shallow depth”? Would they not go off at whatever depth they were set for - presumably, at the depth the destroyer assumed the submarines were lurking?
Submarines have been known to suffer “secondary explosions” caused by internal fires setting off torpedoes after sinking:
Well, if a destroyer is sunk by a uboat the uboat must, by definition, have been close to or on the surface, so presumably in most cases where destroyers are sunk with active DCs, their DCs would be set for shallow depths, as they would probably already have spotted or detected the uboat on or near the surface.
DCs were not usually taken from safe until one were pretty sure to be using them shortly.
The “Kursk” incident you quote on WIKI here was a different sort of thing from what I’m addressing, I think. The Kursk sank due to the explosion in a tube of a dangerous and outdated type of torpedo, whose volatile propellant was prone to explode violently if the torpedo was improperly maintained and handled, as they were on the Kursk. A massive, extremely hot ball of flame blew back into the torpedo room, immolating everyone instantly, then via a poorly-designed ventilation system expanded into the control room and other compartments in the ship, destroying command and control. The Kursk went to the bottom after the reactor was scrammed by some hero in the reactor room, cutting all motive power. On the bottom, the other torpedo warheads in the torpedo room “cooked off,” blowing the bow off the ship. This was relatively shallow water: if the Kursk had been set up on its nose the stern would have been out of the water.
In WW II, depth charges were set at the relatively narrow range of depths possible for submarines of that era. For a Japanese I-200 boat, 360 feet was “test depth,” beyond that they were in unknown territory. For the excellent German boats, crush depth – the End – was @ 600 to 900 feet. Normally, depth charges would be set well above such depths.
You often read about crews of sinking U.S. destroyers killed by their own charges, as it took time to set or “safe” them individually with a hand tool, and they were often left ready for immediate use in calculated risk. For example, the destroyer U.S.S. “Hammann,” sunk by a Japanese submarine alongside the doomed carrier “Yorktown” at the battle of Midway, had her depth charges set when she went down, killing many of her crew in the water – though the destroyer had been alongside the Yorktown providing power and water to fight fires when she was torpedoed. That kind of secondary explosion was generally well-recognized for what it was by observers.
It is the very deep and delayed explosions that I’m interested in here, massive, stunning, and often baffling to experienced and technically well-educated officers on site. These are reported in a number of books on WW II naval action.
No, it doent’t, but the cases where a destroyer was a) chasing a uboat that was at a very deep depth, and then b) was sunk by a different u-boat, are rare, I would imagine.
If a destroyer was sunk by a undetected u-boat or by other means without it actually attacking a deeply submerged boat, its DCs would have been set to safe or shallow depth, as the most common attack modes for both destroyers and aircraft was attacking uboats on the surface or shortly after diving. (Usually followed by more or less guesstimated attacks at deeper depths if the initial attacks failed).
Sometime after WWII, the British navy did a test on a surrendered German submarine to determine its actual crush depth. This depth proved to be, I believe, in excess of 900 feet. In examining the evidence, the Brits found the conning tower hatch in the after torpedo room. It had taken out everything in between. Now that has to be violent!
Should not, but in some cases apparently did. A case in point was the RN battleship HMS Audacious sunk by a hitting a single mine laid by the Germans just north of Ireland near the beginning of WWI. The ship eventually capsized and exploded, believed to have been caused by main battery HE shells falling from their racks and either detonated themselves (the British Lyddite filled shells were known for detonating from shock) or setting off propellant charges they fell into.
Capsizing ships could explode for other reasons. For example the Japanese Yamato suffered a huge explosion after capsizing under air attack in April 1945, enough to knock down one of the circling USN a/c. That was believed to be caused by a fire in a secondary battery turret making it’s way up, originally down, to a main battery magazine after the ship capsized. This kind of event would of course have to be before the ship was all full of water.
As has been mentioned, WWII destroyers and other anti-submarine ships often suffered explosions of their depth charges after sinking. The charges would be set on safe outside of combat zones, but one feature of WWII anti-submarine warfare was how unexpectedly submarines might be encountered over broad areas. And if the ship had to attack a sub instantly, it would most likely be one sighted on the surface at night, the mode in which German and later USN subs made many or most of their attacks, or a periscope would be sighted. An attack against a deep sub would more likely have more warning time as a sound gear contact had first to be refined. Anyway if crewmen couldn’t quickly go and set each active charges back to ‘safe’ in the event the escort itself was suddenly hit, which was sometimes done by heroic efforts, the DC’s would go off when they sank with the ship.
Boilers would also often explode from thermal stress when cold sea water came in contact with the outside, but in water tube boilers in the 20th century had a much lower volume of boiling water than fire tube boilers previously so this wouldn’t be a massive explosive; that would be caused by munitions detonating for one reason or another.
This is what the OP referred to but really a different topic. An implosion by definition isn’t going to create the same kind of disturbance at the surface as an explosion. Hundreds to >1000 feet down, it would be heard on underwater acoustic or seismic devices but there wouldn’t be other evidence.