I
didn’t want to address this but it keeps coming up and people keep getting it
wrong so I guess I’ll have to.
Does
anyone believe that a Mk82, 500 lb (192 lb of explosive filler) aerial bomb has
a 25% larger explosive effect than a 16” high explosive (154 lb of explosive
filler) battleship shell? Of course not,
and yet the Mk82 has 25% greater explosive filler weight. Despite that, a 16” battleship shell has a
profoundly greater explosive effect as demonstrated by the gigantic 50 ft
diameter craters they leave.[5] A Mk82
bomb is not to be sneezed at but it does not produce anything approaching that
kind of effect.
Similarly,
a Naval Strike Missile (NSM) has a 260 lb warhead which is 69% greater than a
16” battleship shell. Does anyone
believe that a NSM has a 69% greater explosive effect than a battleship
shell? Again, of course not!
So,
the 500 lb bomb, with 25% more explosive, has far less explosive impact than a
smaller (by explosive filler weight) battleship shell. How can that be? Shouldn’t the 500 lb bomb, with more
explosive filler weight, produce a much greater effect than a battleship shell?
The
answer/explanation is a combination of chemistry and physics. Note, this is not a doctoral thesis and few
of us are chemists or physicists so I’m going to simplify the following
discussion for general audience comprehension.
Explosive Effect
Definition
To
begin, we need to define what an ‘explosive effect’ is. There’s nothing magical or complicated about
it. It is simply the degree of destruction
caused by the explosion. A hand grenade
has a small explosive effect compared to a 500 lb bomb. See?
Nothing complicated. But, if it’s
that simple, how do we explain the bigger destructive effect of the 16” shell
versus a 500 lb bomb that has more weight of explosive filler?
Chemistry and Physics
This
is where we begin to delve into the chemistry and physics of an explosion (see
Ref [6] for a detailed discussion of explosive chemical and physical
properties). Explosive effect is the
damage inflicted on the target via a combination of overpressure (an
instantaneous pulse of pressure far above normal atmospheric pressure), heat
(the exothermic chemical reaction of the explosive), and physical damage by
bomb/shell fragments (shrapnel), among other mechanisms. Of these, pressure is the main destructive mechanism
for general explosive munitions. So, how
is overpressure (increased pressure) generated?
We’ll
answer that with a couple illustrative examples that lie at the heart of the
matter and which we’ll keep referring back to.
Gunpowder – Gunpowder
explodes, right? Well, sure. We’ve all seen hundreds of movies where
barrels of gunpowder are ignited and explode.
Before we move on from this seemingly obvious phenomenon, let’s recall
that we’ve also seen hundreds of movies where a trail of gunpowder, sprinkled
on the ground, is ignited and slowly burns (acting as a fuse) rather than
explodes. Wait a minute, I thought
gunpowder explodes? Why does it burn on
the ground rather than explode?
Gasoline – Gas explodes,
right? Or does it? If gasoline, spilled on the ground, is
ignited, what happens? Does it burn or
explode? It burns! However, if gas in a confined tank is
ignited, it explodes!
Do
you see the pattern – the key - behind this explode or burn phenomenon? It’s confinement (containment). When ‘explosive’ materials are
confined/contained, they explode. When
they’re unconfined, they burn.
Now,
what is it about confinement/containment that makes something explode rather
than burn? Again, it’s chemistry and
physics!
Burning
is actually a chemical reaction (oxidation).
A material reacts with oxygen at a very fast rate (an example of an exceedingly
slow burning reaction rate would be rust!).
An explosion is the exact same chemical oxidation reaction but occurring
in a confined/contained housing (the bomb or grenade or missile).
Let’s
dig deeper.
When
something burns, it undergoes a chemical reaction that releases gas as a
byproduct. In an open
(unconfined/uncontained) environment – like gunpowder or gasoline on the ground
– the released gas is harmlessly dispersed.
No damaging pressure build up can occur.
Conversely, in a confined/contained environment – like the inside of a naval
shell – the released gas has nowhere to go and, as the burn continues and more
and more gas is released, the quantity and, therefore, pressure of the
confined/contained gas increases until, eventually, the pressure of the gas
exceeds the strength of the container (the shell, bomb, grenade, or missile)
and causes the container to burst which is the explosion we see. This burst instantaneously releases the pent
up pressure (now an overpressure wave) and heat. In addition, the released pressure wave
scatters the bomb fragments (shrapnel) and damage occurs to the surrounding
area and objects.
The
longer the pressure build up is contained, the higher the pressure gets inside the
container and the greater the magnitude of the pressure wave when the container
finally bursts and releases the pressure.
This is the overpressure blast wave which causes so much damage. The overpressure wave causes objects around
the explosion to be fractured, bent, twisted, ripped loose, and flung about.
Interestingly,
if the container is stronger than the ultimate built up gas pressure, nothing
happens. This is what a bomb disposal
chamber does. It remains intact and
contains the entire explosive force, releasing nothing. The explosive gas can then be vented in a
slow, safe, controlled manner.
Of
course, the actual chemical composition of the explosive is important
(different reaction rates, for example) but that’s beyond the scope of this
post.
Shell versus Missile
Construction
Now
that we understand the importance of containment in producing an explosive
effect, let’s examine the construction of various munitions.
Naval
shells are intentionally constructed of very thick walls with relatively small
burst charges of explosive material. As
we just discussed, the burst charge is greatly amplified by the containment of
the heavy wall.
Battleship
16” shells have wall thicknesses of around 3+ inches. A 9.3 in diameter naval shell (type/gun
unspecified) had a 2.5 in thick wall.[2]
And so on.
 |
| 16" Battleship AP Shell Cutaway |
 |
| 16" Battleship HC (HE) Shell Diagram - note the shell wall thickness of 3+ inches |
 |
| Harpoon Missile Cutaway - note the thin sheet metal covering |
We
see, then, that the missile’s overall weight is consumed by fuel, guidance
mechanisms, electronics, telemetry, sensors, fins and deployment mechanisms,
and fuzes. A naval shell has nothing inside it other than a fairly simplistic
fuze and, of course, the explosive chemical. All the naval shell's
non-explosive weight goes into the wall thickness. Thus, a battleship’s 2000 lb
weight is 154 lb of explosive filler and 1846 lb of wall. That’s a lot of containment! In contrast, the missile "wall" is
nothing more than a sheet metal container.
Bombs
lie in between shells and missiles and vary widely. Some have heavy walls, though not generally approaching
naval shells, and some do not.
 |
| Mk 82 Bomb Cutaway - note the reduced wall thickness compared to a naval shell |
Body Wall of 0.5" to 1": Bursting Charge x 5 = Effective Explosive Weight
Body Wall of 0.25" to 0.5": Bursting Charge x 2.5 = Effective Explosive Weight
Body Wall of <0.25": Bursting Charge = Effective Explosive Weight
[a]The reader offered this disclaimer: “All figures are just from my memory, mind you, and shouldn't be taken as decisive fact (nor should any rule of thumb), but it is illustrative of the general idea.”
The High Capacity (HC) [16”] shell can create a crater 50 feet wide and 20 feet deep (15 x 6 m). During her deployment off Vietnam, USS New Jersey (BB-62) occasionally fired a single HC round into the jungle and so created a helicopter landing zone 200 yards (180 m) in diameter and defoliated trees for 300 yards (270 m) beyond that.[5]
“The crater from a 500-lb. bomb with impact fuze (e.g., MK 82) is typically 30 feet in diameter and 15 feet deep (this obviously varies greatly with the terrain)” (Doleman Jr., Edgar C., 1984. Tools of War. Boston Publishing Company, Boston) ; note: this quote is unverified by me but the book exists and there is no reason to doubt it
A conventional 155mm artillery high explosive (HE) shell often produce a crater about 1.2–1.5 meters deep and 4–5 meters wide (4). The M114 howitzer of WWII used an HE shell with around 15 lb of explosive. The modern 155 mm M795 shell has around 24 lbs of explosive.
A 16-inch (406 mm) shell fired from an Iowa class battleship created a crater about 6 meters deep and 15 meters wide (4)
http://www.navweaps.com/Weapons/WNUS_61-62_ags.php
https://maritime.org/doc/ordnance/index.htm
https://www.quora.com/How-large-would-a-detonation-from-a-800mm-artillery-shell-make-compared-to-other-munitions
http://navweaps.com/Weapons/WNUS_16-50_mk7.php
Published: 27th International Pyrotechnics Seminar, July 2000
https://psemc.com/resources/pyrotechnic-white-papers/properties-of-selected-high-explosives-rev/
Thanks for that it was very interesting.
ReplyDeleteGreat write up. Now continue the physics and realise that a ship's gun can deliver thousands of heavy walled shells while aircraft are severely limited in the weight they can carry. Most bombs generally do not penetrate but instead are for soft targets (troops and unreinforced buildings) so they do not get the compounding effect of the explosive in a contained space. Thin skinned targets (tank tops) do get the compounding effect but are hard to hit with gravity (even smart ones) bombs.
ReplyDeleteEven artillery can deliver heavy more destructive shells than aircraft bombs because the ground supports them much easier than flying.
"Now continue the physics and realise that a ship's gun can deliver thousands of heavy walled shells while aircraft are severely limited in the weight they can carry"
DeleteYes, we did this in, "Carrier and Battleship Throw Weights"
A 16-in gun fires lots of mass Mach 2.
ReplyDeleteFrom google:
Kinetic energy is a form of energy that an object or a particle has by reason of its motion. If work, which transfers energy, is done on an object by applying a net force, the object speeds up and thereby gains kinetic energy. Kinetic energy is a property of a moving object or particle and depends not only on its motion but also on its mass.
----------------------------
The Meteor Crater in Arizona was created just by Kinetic energy.
https://www.space.com/meteor-crater-hole-from-space-lunar-surface
I've thought about covering a facility with a big fence/dome that would cause cruise missiles to explode on contact.
One needs to be cautious about ascribing mythical properties to kinetic energy. For example, many people believe that the kinetic energy, alone, of a projectile travelling at Mach+ speeds will vaporize whatever it hits and, generally, this is simply not true. We've done actual calculations on missiles and super-cavitating torpedoes and found that the kinetic energy contribution is relatively small compared to the explosive. We've also discussed the bullet-paper phenomenon.
DeleteTo be fair, you haven't made any 'vaporization' claim and I'm just using your comment remind people about kinetic energy so that we don't encourage incorrect beliefs. Thanks for allowing me to do so!
"I've thought about covering a facility with a big fence/dome that would cause cruise missiles to explode on contact."
We've done that in various forms. Cage armor is one example. The 'de-capping' deck on a ship is another.
Of course, the quick and easy counter to such a dome is a delayed fuse mechanism.
The AP round had less than 100lbs of HE, so kinetic energy did the damage.
DeleteSince cruise missiles are unarmored, Mach speed impact on a metal cage should cause the warhead to explode regardless of the fuse.
"The AP round had less than 100lbs of HE, so kinetic energy did the damage."
DeleteWell, let's do the calculation. The formula for kinetic energy (KE) is
KE = 0.5(m x v2); where m=mass and v=velocity
Using a mass of 2000 lb for the shell and a velocity of 2500 ft/s (muzzle velocity; impact velocity would be slower but we'll use muzzle velocity since I don't have a readily available, better figure)
KE = 0.5(2000 lb x 2500 ft/s x 2500 ft/s)
rounding an converting to joules,
KE = 263,000,000 J
By comparison, a kg of TNT releases 4,184,000 J. Thus, the KE of the AP shell is equivalent to around 63 kg (139 lb) of TNT. That's not a lot compared to the observed effects! Kinetic energy effects of a AP shell are actually fairly minimal and tend to be focused on the armor penetration (drilling a hole through the armor, to express it crudely) rather than general damage. The general damage is done by the shell burst.
"Mach speed impact on a metal cage should cause the warhead to explode regardless of the fuse."
Why? Lots of air-dropped bombs fail to explode and, while that's not impacting at mach speed, it's still a very high velocity impact and it doesn't necessarily cause explosion. /Explosives actually tend to be fairly stable and somewhat difficult to ignite or else they'd keep blowing up in storage!
The containment effect is what gives shells their boost in effect. I wonder how much work has gone into better nad more effective materials to contain the blast. Potentially this could give better results for all categories of muntions.
ReplyDeleteThere is a balance to this. If the walls are too strong, the blast effect is diminished or prevented (bomb disposal chamber). You want the pressure to build to a peak but not go past that point to the side of reduced effects.
DeletePerhaps you're suggesting stronger walls with reduced thickness due to advances in metallurgy? That would certainly be worthwhile; to accomplish the same concentration using a lighter shell. Imagine a battleship shell that only weighed 1000 lb. Of course, the overall weight is also a positive in terms of kinetic energy so maybe reducing weight isn't a good thing? I don't know. This is where you need explosives experts to weigh in (pardon the pun).
Interesting thought... If we could have the blast containment spec of an AP shell, would we lose penetration?? Not that a 16in shell of any kind needs maximized penetration against any afloat targets since everything is thin skinned. But for shore installation work...(??) And another thought- if the case was made of significantly lighter material- what kind of range increase could we see???
Delete"blast containment spec of an AP shell, would we lose penetration??"
DeleteIs there a missing word in that sentence or am I missing what you're asking? Battleship shells came in two general types: AP and high explosive (HC/HE). The HC had similar thick walls but didn't have the heavy nose cap which allowed for armor penetration. Because the HC didn't have the nose cap, it had a little more explosive filler compared to the AP. This is all thoroughly described and documented on the NavWeaps site.
I may be missing the thrust of your question and, if so, I apologize and please try again!
As far as range increase from a lighter material, that's a fascinating question for which I have no answer.
Just for fun, I plugged the battleship shell numbers into a ballistic range calculator and by increasing the initial muzzle velocity from 2500 fps to 3000 fps (which is where the lighter weight would come into play), the range increases by around 16 miles.
For the powder charges used and the barrel diameter and caliber, what is the maximum muzzle velocity obtainable? Again, I have no idea!
Apologies- that wasnt very clear. I was just wondering if an alternate material, which provided us with the same blast containment as an "old" shell, would/could also provide the same penetration. In retrospect thats likely an impossible, unanswerable question, but we both see the benefits of a new lighter case material. I think we're onto somthing here!!! Your calculated 16 miles of range is a game changer!!. Just calling it 10+, thats basically a 50% increase in range!!! It would certainly keep ships doing shore bombardment out at a safer range. Is it highly important to increase the range?? Maybe, but thats debateable. What can we do at 32 miles that we cant do at 22 except a bit more comprehensive shore remodeling?? Does it give us domination of, or put us out of range of- any enemy-fielded systems?? I suppose as long as the new shells dont get hyper expensive ala'-AGS, then its certainly an avenue to look at further.
Delete"would/could also provide the same penetration"
DeleteI would think not. Bear in mind that we're discussing two separate characteristics of a naval shell:
1. Containment to amplify the explosion.
2. Penetration of armor.
The former requires uniformly thick walls. The later requires a very heavy nose cap.
A theoretically lighter material might contain and amplify the blast but a lighter nose cap would defeat the purpose of the nose cap and degrade penetration ... ... I would speculate.
I was thinking more along the lines of five inch shells and missiles. That's probabably where improvement in destruction would be most useful. But yeah even the bigger stuff being a bit nastier could be that difference between success and not,
Delete"I didn’t want to address this..."
ReplyDeleteI'm glad you did. This is interesting and helpful.
Thanks for that feedback! One of my secondary goals for this blog is to remove the mystery and misunderstandings from many of the naval issues that suffer from 'institutional confusion' so that discussions can be more logical and productive. I'll keep trying!
DeleteThis is why as a Combat Engineer, we buried explosives instead of a surface detonation. It's known as"tamping". Allows the expanding gas bubble to reach significantly higher pressure before being released . And you're correct. Explosives do not "explode". They flash to a gas, and it's the expanding gas bubble and resulting shockwave that does all the damage. The thermal effect is inconsequential in comparison. Shaped charges and explosively formed projectiles are an entirely different effect, and a different discussion for another time.
ReplyDeleteDefinition of tamping
Deletei. The act of inserting and packing explosives and stemming in a shothole.
See Also: stemmer
ii. The act of packing a drilled hole around a cartridge with fine dirt from the floor of a mine before blasting, to prevent a misdirection of the force of the blast.
Ref: Korson
iii. The material placed over a charge in a borehole, to better confine the force of the explosion to the lower part of the hole.
The definition of Tamping. As a reference
Interesting and it makes perfect sense. Thanks for chiming in!
DeleteDo we see the same effect with a bunker buster bomb that explodes underground in a semi-contained fashion?
To Combat Engineer,
DeleteFor fine example of tamping see Barnes Wallace and Upkeep bomb, the water was the tamping, the spin got the bomb to stay next to dam wall, then boom.
Mythbusters, had many many examples of contained vs. uncontained explosions and their pressure effects.
DeleteThe GBU-28 bunker buster in the first Gulf war was surplus 8inch howitzer barrels due to the extremely compressed timeline for development and deployment. I'd suspect bunker busters use a thicker case than a GP bomb due to the need to pass through reinforced concrete for significant depths before detonation instead of pancaking against the bunker surface. And the newest generation is thermobaric, which relies entirely on massive over pressure to collapse tunnels and cave networks.
DeleteThere is also the Tallboy and Grand Slam series "earthquake" bombs from WW2.
Deletehttps://en.m.wikipedia.org/wiki/Earthquake_bomb
Interesting. This would further suggest a shift back to shells if ships gained armor once again. The thicker shells give you armor penetration and more explosive force.
ReplyDeleteOne alternative history question is what if in the 1980s anti ship missiles had hit a heavily armored battleship or cruiser instead of lightly armed frigates, tankers, destroyers, or Russian piles of junk. Would that one event swing perceptions?
"This would further suggest a shift back to shells if ships gained armor once again."
DeleteYes. However, no navy seems to be giving armor any thought, whatsoever, for reasons that baffle and elude me.
"One alternative history question is what if ... anti ship missiles had hit ... Would that one event swing perceptions?"
I don't know about that but when navies start losing billion dollar frigates (or destroyers) to low end, relatively lightweight missiles, you'll see a rapid 'rediscovery' and love affair with armor.
Investing a billion+ dollars into a ship and then not protecting it with armor was a dead end, fool's branch on the ship evolutionary road. What a bunch of idiots we have designing ships!
It does seem like warships are missing an evolution. Tanks responded to shaped charges with composite armor. I can see where that might not be appropriate for a large ship, but large ships aren't space and weight constrained like tanks. There have to be tradeoffs out there that work. Especially since the labor productivity for building hulls has increased significantly since WWII (though obviously less in US shipyards).
DeleteYou could use double hulling and fill up a meter gap with clay/sand mixes as an extreme example. It'd be heavy but relatively inexpensive and simple.
On the other hand, while ships dont use armor (passive defense), they have Active Protection Systems like tanks. Consider the Russians, who had the Shtora IR jammers and hardkill APS systems; on warships, you have softkill defenses (EW, decoys) and the hardkill defenses (interceptor SAMs, CIWS).
DeleteYes, active defenses are important. The main lesson I draw from tanks is that it takes all the systems working together. They couldn’t keep adding fancier armor forever. At some point it was more effective to add systems like Trophy. And tanks without infantry and artillery support die quickly. They still get hit and take losses so crew protection and repairability are key features.
DeleteOur ships might be a lot more effective if they had better passive protection. Active defenses wouldn’t need to be perfect or kill every missile outside of shrapnel range. Ships need to operate in large groups for better protection. It is hard to say our ships are easily repairable or adequately protect the crew after attacks like the USS Cole. It takes more than active defenses even though they are wonderful.
"On the other hand, while ships dont use armor (passive defense), they have Active Protection Systems like tanks. "
DeleteIn a manner of speaking, I guess. One major difference is that tank active protection systems claim to be near 100% effective (I don't know what the actual success rate is) whereas ship systems (Standard, ESSM, RAM, CIWS) are proven to be nowhere near 100%. They're closer to 10-20%. Thus, armor is desperately needed ... like tanks (to complete the analogy!).
Something to think about ... ...
ReplyDeleteSince no ship has armor today, imagine the destructive power of a 16" HC (high explosive instead of armor piercing) shell with a slightly delayed contact fuse so as not to pass through a thin skinned ship? It would likely be a single hit, total destruction on a modern frigate/destroyer.
*physically flinches
DeleteOuch!!!
Id of donated a Spruance for THAT SinkEx!!! (Not that they shouldnt all be in reserve right now, but if they were destined to be sunk, thatd of been worthwhile)
You don't really have to think about it. I wish we had more information when the USS Iowa sunk the Japanese Katori by firing 46 HE shells into her.
DeleteI know wiki isn't considered the gold standard of publishing but this is what they report.
At an average range of 14,500 yards (13,300 m), Iowa closed with Katori and fired 46 16-inch (406 mm) high capacity (non-armor-piercing) rounds and 124 5-inch (127 mm), straddling the cruiser with eight salvos. CAG 17/A16-3 reported Iowa hit Katori with her second salvo. Just after Iowa's fourth salvo, Katori quickly listed to port exposing seven large shell holes about 5 feet (1.5 m) in diameter in her starboard side, one under the bridge about five feet below the waterline, another amidships about at the waterline, plus about nine smaller holes.[2] The damage on the port side was much worse. After being under attack by Iowa for about five minutes, Katori sank stern first, with a port side list.
That means those shells sunk the cruiser from engagement to sinking in 5 minutes. The results speak for themselves. Todays warships would share the same fate.
https://en.m.wikipedia.org/wiki/M1156_Precision_Guidance_Kit
ReplyDeletehttps://en.m.wikipedia.org/wiki/Rocket-assisted_projectile
https://en.m.wikipedia.org/wiki/Base_bleed
https://man.fas.org/dod-101/sys/land/macs.htm
Land artillery has some upgrades that could very well be applied to naval cannon shells without much beyond scaling simply due to shell diameter and weight
I've made this comparison on a previous post about armore, and I'd like to make it again. A few centuries ago, firearms became the primary battlefield weapon. The armor that protected well against bladed weapons did little to protect against a bullet. Throughout the 1700-1800's, little to no armor was worn on the battlefield. As explosive weapons became prevalent, many casualties were caused by indirect fire (shrapnel and flying debris). By the time of WWI, the simple steel helmet was standard issue in most armies. Nearing the end of the 20th century, kevlar vest and other protective gear became common. The modern protective gear won't protect the soldier against everything, but it will stop most of the small stuff.
ReplyDeleteAfter WWII, nuclear weapons were the next big thing. A ship's amor can't stop a nuclear blast, so why even bother? The issue is; how likely is a ship to get hit with a nuclear weapon versus a conventional weapon which it could guard against? I think after the next large deep water naval battle, we'll see ship armor come back in style. "If only that ship had some amor to protect vital points, it could have kept on fighting, and maybe we would have won that battle."
Meant to sign the above as my user name MM-13B
Delete