In an explosion, the air blast shock wave is the primary damage mechanism,
and certainly enough to break a car into pieces.
But that shockwave, even though powerful, would not be able to penetrate through a heavily armored
vehicle. This is why when anti-tank rockets detonate, they do something a little strange.
This anti-tank rocket is likely already moving faster than the speed of sound,
but notice what happens when it explodes.
Aside from the blast, something much more significant is happening,
shooting forward at hypersonic speeds, anywhere from 4 to 8 miles
per second! and that can cut through the thick armor of a tank, like it’s butter!
But where that hypersonic jet of destruction comes from, what could be done to protect against it,
and why that same jet is used in the design of nuclear bombs, is Not What You Think!
As soon as tanks entered the scene in WWI, attempts to develop weapons that could penetrate
through the tanks’ thick armor emerged. Early anti-tank rifles relied primarily on
kinetic energy of metal shells to pierce through the armor.
To protect the tanks, thicker and more effective armor was added,
and to pierce through the thicker armor, anti-tank guns became increasingly heavier.
This back and forth one-upping resulted in larger and heavier anti-tank guns that had to
be mounted on wheels and towed around, making them unusable for infantry that was on foot.
Realizing this restriction, Armies needed to come up with a human-portable anti-tank weapon.
During WWII, Soviets developed RPG-43, a hand-held anti-tank grenade.
Just to clarify a popular misconception, RPG does not stand for "Rocket Propelled Grenade".
RPG is a backronym. The actual acronym stands for Ручной Противотанковый Гранатомёт,
which means handheld anti-tank grenade launcher.
Even though RPG-43 could pierce through thick armor, the Soviets
first had to solve a bigger problem. Being a hand-thrown grenade weighing about 3 lbs,
soldiers had to get dangerously close to tanks in order to throw the RPG-43.
What was needed was a way to deliver the grenade from a distance.
So the Soviets came up with a cross-over between the American Bazooka and the German Panzerfaust.
The Bazooka was reloadable, as opposed to the Panzerfaust, which had a one-time use launcher.
But Panzerfaust’s big advantage was that its warhead would sit outside the launch tube,
as opposed to the Bazooka, where the entire round had to be completely loaded into the launcher.
This would limit the size of the warhead that a Bazooka could launch,
and as you’ll see, that size is extremely important.
Enter the Soviet RPG-7, the most widely used RPG in the world, which solved the
problem with hand-thrown anti-tank grenades, as they could now be launched from far away.
But what was the difference between regular grandes and anti-tank grandes
that allowed them to penetrate through the thick armor of tanks?
A regular grande is an explosive charge with a metal shell wrapped all around.
The shockwave from the explosion tears the metal shell into pieces,
launching shrapnel in all directions, which could be fatal for those in proximity.
But to penetrate through armor, something more surgical is required.
RPG rounds fall under a special type of explosive charge, known as shaped charges. Not so much the
outer shape, but the inner shape of the explosive charge. Inside both, the hand-thrown RPG-43 and
its rocket-propelled variants, there is a metal liner that forms a cone-shaped cavity.
There are explosives packed behind the liner. Upon contact with the target, the charge is detonated,
which creates a pressure wave behind the metal liner. This in turn deforms the liner in a way
that generates a focused jet of metal particles that shoot straight out at hypersonic speeds.
It’s purely the kinetic energy of the jet, not the shockwave
from the detonation, that penetrates the armor.
The effective penetration depth of the jet is 7 times or more, the diameter of the shaped charge.
This is why having the warhead mounted outside of the launch tube gave RPGs a big advantage
over Bazookas. The RPGs’ larger diameter warhead could cut through thicker armor.
Once this hypersonic projectile hits the interior of the tank, it causes utter devastation,
killing those inside and possibly cooking off the tank, causing the ammunition inside to explode.
But shaped charges have an Achilles' heel.
In 2017, the city of Marawi in the Philippines was a battleground for 5 months,
where government security forces fought against a number of militant groups tied to ISIS.
The militants had RPG-2s, an older model that is not well-suited to destroy modern tanks, but they
had enough punch to destroy the thinly armored personnel carriers of the government forces.
Faced with this unexpected threat, the security forces had to improvise.
They covered their lightly armored vehicles in slats of wood and even packs of cardboard.
Now if you think there is no way that some thin layer of wood is
going to stop the penetration from a round of RPG-2, you are right!
The wood and cardboard cannot stop a hypersonic jet of metal, but they can make it less effective.
See, the hypersonic jet generated from the explosion of a shaped charge, is extremely
powerful, but only for a short distance. The farther the shaped charge explodes from its
intended target, the less damage it can inflict. Adding slats of wood and packs of cardboard
creates a gap between the warhead and the vehicle at the time of detonation. That gap, even
though small, was enough to help the Philippine government’s security forces defeat the militants.
The metal cages around tanks and other armored vehicles are there
specifically for this reason. To cause a premature explosion!
But that is not enough protection against modern anti-tank weapons.
These metal boxes are Explosive Reactive Armor, and are supposed to counter anti-tank weapons.
Inside the boxes, there is a special type of explosive. You can drop them, shoot at them,
and even set them on fire. But they won’t explode. And you wouldn’t want them to. Because if a
machine gun could easily detonate all the boxes, it could strip the tank off of all its protection.
So why is it that anti-tank rounds could set off the boxes, but not bullets?
The answer is that the explosives inside these boxes are insensitive, meaning the only thing that
would set them off, is an extremely powerful shockwave, not shrapnel, bullets or heat.
That’s why you see footage of tanks that are burned down,
but the boxes of reactive armor have remained unexploded.
C-4 is an example of insensitive explosives, which is used in some types of explosive reactive armor.
The insensitive nature of this category of explosives make
them ideal – not only as armor for tanks, but also other things that
you really wouldn’t want to set off by accident, like nuclear weapons!
To sets off a nuclear weapon, the core of the bomb has to be compressed until it reaches criticality,
which sets off a chain reaction that ultimately generates immense amounts of energy in a very
short period of time. That's a blast! That initial compression of the core
is done using shaped charges, the same concept that is used in RPGs.
An array of shaped charges are organized into what’s called an “explosive lens”.
Similar to how an optical lens focuses light waves, an explosive lens focuses
the detonation waves into a spherical shape, which compresses the core until it reaches criticality.
But it is extremely important that the explosive lens doesn’t detonate
prematurely. And the US government had to learn this the hard way.
When nuclear armed B-52 bombers crashed in Palomares in 1966
and at Thule Air Base in Greenland in 1968 as part of Operation Chrome Dome,
those investigating the scene of the accidents became extremely concerned.
The high explosives used in the nuclear bombs had detonated on impact, even though luckily, the
nuclear devices hadn’t gone off. So the Americans started the research and development of explosives
that were stable enough to withstand the forces involved in a plane crash. And they came up with
a safer type of explosive, called Insensitive High Explosives to be used in nuclear weapons.
These new explosives could withstand impacts up to 1,500 feet per second,
compared to conventional high explosives which would detonate at only 100 feet per second.
Explosive Reactive Armor is basically made up of insensitive explosives sandwiched
in between two metal plates. An explosive sandwich if you will!
When an anti-tank weapon comes in contact with Explosive Reactive Armor,
its shockwave is powerful enough to detonate the insensitive explosives,
which shoots out the outer metal plate toward the projectile. This further increases the space
between the hypersonic jet of metal and the tank’s armor, and prevents the destruction of the tank.
But Explosive Reactive Armor doesn’t stand a chance against modern anti-tank weapons, like
Javelins. That’s because the Javelin has a tandem warhead, meaning that it has two explosives.
The first explosive is spent on neutralizing the tank’s reactive armor.
It’s the second explosive that delivers the lethal damage. So … what now?!
We may have reached a point where we can’t simply add more armor in order to protect ground vehicles
against threats. The modern anti-tank weapons have overmatched what passive or reactive armor can do.
What is needed is active protection systems, specifically hark-kill systems, which can
detect incoming threats, and then neutralize them before they ever get to the vehicle.
That said, even though a variety of active protection systems already exist,
not all of them can handle top-attack anti-tank missiles,
like the American Javelin and the German PARS 3, which plunge down onto their targets.
It seems like the utility of tanks is reducing. A tank costs 5 to 10 million dollars, excluding its
active protection system, which costs another 1 to 2 million. But a round of Javelin costs less than
$200,000, and even an active protection system would be hard pressed against multiple Javelins.
The balance has shifted from tanks toward infantry, both effectively and economically.
It remains to be seen whether tanks will be able to shift the scale back in their favor.