Offensive Weapons Can Overcome Any Passive Defense
There is no tank (or other armored vehicle or mobile ground based military system) on Earth that can't be destroyed with a hit from a single anti-tank missile launched from a device about the size of a golf club bag, that comes close to a one shot, one kill ratio, and has a range longer than the range of a tank's main gun. Often, it takes less to at least disable even a heavily armored tank, like a well placed tank round, an extended barrage of 25-40 mm canon rounds, some land mines, mortar and artillery rounds, IEDs, or even a well placed hit from a rocket propelled grenade or recoilless rifle, although heavy tank armor is pretty much impervious to small arms fire from assault rifles, machine guns, and the like.
There is no warship on Earth that can't be destroyed with a hit from a single, typical, anti-ship missile, which can have a range of 100 miles or more, and can be fired from land, from other surface ships, from submarines, from fighter aircraft, from bomber aircraft, from maritime patrol aircraft, and even from cargo aircraft like the C-17 and military helicopters. One or two torpedoes, or bombs are also up to this task. So are many anti-ship mines.
A variety of torpedoes, sea mines, and anti-submarine missiles are capable of destroying or disabling any military submarine in the world with a single hit.
Most air to air combat involves the launch of a single guided air to air missile that the target aircraft is aware of for a few seconds before it hits, but too late in the vast majority of cases to evade. Jet aircraft sometimes evade air to air missiles or surface to air missiles fired within the range of the missile, with flares and extreme maneuvers, but this is the exception and not the rule to the point of being a minor miracle.
The largest conventional bomb in U.S. service at the moment, the MOAB has an explosive yield of 11 tons of TNT and a 0.6 mile blast radius (deployed via a C-130 intra-theater transport plane). This is about the same as the smallest nuclear weapons every built (which weighed about 60 pounds). While it may not literally be able to bust any bunker or fortification, it will destroy pretty much any building not buried deep within a mountain or deep underground.
The only modern aircraft to have any meaningful armor protection is the A-10 fighter, which while not really effective against modern anti-aircraft missiles provides meaningful protection against small arms fire from ground troops, shrapnel, and perhaps even somewhat against anti-aircraft guns firing grenade sized canon rounds. Other military aircraft rely entirely on active defenses (including staying out of range of enemy fire, and hiding and dodging).
Active Defenses
Because there are viable means of defeating any kind of passive armor that are available to pretty much any national military force worth its salt, and even select non-governmental insurgent forces (e.g. the Houthis right now, or the Afghan insurgents during the insurgency against Soviet rule there), war in the 21st century against any opponent of this caliber is all about not getting hit in the first place.
Hide and Dodge
One approach is to hide and dodge.
For example, it is now standard for artillery forces to "shoot and scoot" before the volley of fire it launched is used to identify its location and fire back destroying it.
A few U.S. aircraft currently in service (the F-22, the F-35, the B-2, and soon the B-21, as well as the out of service F-117), and possible a few very new Chinese and Russian planes, have radar stealth. But they can still be seen visually if one is close enough, they have significant heat signatures, make lots of noise, and have locations that can be tracked back from the bombs and missiles they drop.
The SR-72 Blackbird spy plane can outrun and can stay about the maximum altitude of many war planes and even missiles, but it has no great offensive capabilities.
Submarines are good at hiding. Non-stealth aircraft, surface warships, and tanks, are not. Tracked vehicles and surface warships and submarines are all extremely slow. Wheeled vehicles are faster but don't rival missiles or aircraft. Helicopters, most smaller drones, and many transport aircraft are still much slower than a missile or a jet fighter.
Camouflage can help a little, but only on the margins in most cases for large military systems, as opposed to individual soldiers.
Confuse
In the face of guided missiles and "smart bombs" and drones (and sometimes even manned aircraft), electronic jamming, dazzling visual sensors, sending out decoys and/or covering smoke, or even hacking the guidance system is sometimes possible. Indeed, these confusion oriented defenses are sometimes called "soft kill" active defenses.
U.S. Navy destroyers also have some soft kill type electronic warfare active defenses against income drones, smart bombs, and missiles, and torpedo defenses that use both soft kill electronic warfare type jammers, and decoys, all of which are active defenses designed to confuse incoming ordinance.
F-15 fighters sometimes carry ADM-160 MALD missiles which have electronic countermeasures and are used as decoys. Many aircraft have flare systems designed to be used as decoys against heat seeking anti-aircraft missiles.
Hard active defenses
Finally, there are "hard" active defenses, that destroy incoming ordinance before it gets too close.
Lasers
Laser weapons (and other directed energy weapons like microwave beams) are a class of "hard" active defenses that are just about ready for viable use on the battlefield. They prematurely ignite fuel or explosives, destroy guidance systems, or melt critical control surfaces. No practical laser weapons have the punch to pierce tank armor or sink a blue sea warship, but they can, in principle, prematurely ignite an incoming missile or artillery shell or naval gun shell or even a tank main gun shell, crash a drone, and can disable a speed boat or even a helicopter. It could even cause an externally carried bomb or missile on a fighter aircraft to explode and disable it. But the faster moving a target of a laser weapon is, the harder it is to get enough beam time on target to destroy it before it destroys you, during the possibly brief window when the target is in a line of sight.
Boeing's 5 kilowatt laser (shown above with the image from this link) intended for Army use against smaller drones, it typical of the state of the art, although these are still very novel and I'm not aware of any actually use of them in combat yet. There are some similar lasers that have been deployed on select U.S. Navy ships and experimentally in the Army up to 50 kilowatts.
Why military lasers are so low powered is a question I don't have an answer for. I have burners on my kitchen stove that use more than 5 kilowatts. There are ordinary civilian electric cars that use 350 kilowatts at full acceleration. There is no reason that I can see that a military laser defending a naval ship or forward operating base shouldn't have at least 1 megawatt of power, which would greatly reduce the amount of time that it would need to dispatch each target, making it more effective against swarms of targets and fast moving targets.
The pros of a laser weapon are that it is the cheapest per successful kill ($10 or so of electricity; it would still be cost competitive at 200 times that price), can be powered with batteries or super-capacitors charged with a military system's existing electrical power sources (so in the long run, its ammunition supply is basically unlimited), and the weapon itself isn't particularly large or expensive to build relative to conventional military guns. Improved battery technology may make it more viable going forward.
The cons are that the lower the wattage the more time the beam needs to be on target to destroy it (which makes it ineffective against targets that are approaching too fast like hypersonic missiles), it needs an energy source such as a battery or super-capacitor that is quite substantial (the exact demands depend on the wattage of the weapon), it can only hit targets in a line of sight (and struggles beyond about 2 miles in many cases), and it can be impaired by dust, smoke, rain, or mist.
Still, laser weapons could soon be a standard part of a layered active defense system. A powerful enough laser weapon could give an armored vehicle a fighting chance against an incoming anti-tank missile. It could be well suited to protecting a military base or artillery battery or naval ship against an incoming kamikaze drones or artillery shells or missiles. A fighter jet with an anti-air missile coming at it might be able to use a strong enough laser to shoot the income missile out of the sky before it hits, while it is trying to evade.
Guns
Another option is a "slug thrower" that fires "dumb" or minimally "smart" rounds (like grenades with timed fuses or proximity fuses).
Historically, this was the idea behind cannon artillery style anti-aircraft guns, which are now mostly obsolete because of their limited range against high altitude fighter and bomber aircraft.
The main example of this approach in the modern U.S. military is the Phalanx Close In Weapon System (CIWS) that shoots a rapid barrage of 20 mm (i.e. grenade sized) cannon rounds set to explode at a certain range if it doesn't make contact at incoming missiles and shells and drones. This was originally designed for the U.S. Navy where it is intended as a last line of defense against income missiles, and is in place on many U.S. warships, although a U.S. Army variant for point defense has also been developed on a limited basis.
The Phalanx CIWS (SEE-wiz) is an automated gun-based close-in weapon system to defend military watercraft automatically against incoming threats such as aircraft, missiles, and small boats. It was designed and manufactured by the General Dynamics Corporation, Pomona Division, later a part of Raytheon. Consisting of a radar-guided 20 mm (0.8 in) Vulcan cannon mounted on a swiveling base, the Phalanx has been used by the United States Navy and the naval forces of 15 other countries. The U.S. Navy deploys it on every class of surface combat ship, except the Zumwalt-class destroyer and San Antonio-class amphibious transport dock. Other users include the British Royal Navy, the Royal Australian Navy, the Royal New Zealand Navy, the Royal Canadian Navy, and the U.S. Coast Guard.A land variant, the LPWS (Land Phalanx Weapon System), part of the Counter Rocket, Artillery, and Mortar (C-RAM) system, was developed. It was deployed to counter rocket, artillery and mortar attacks during the 2021 US withdrawal from Afghanistan. The U.S. Navy also fields the SeaRAM system, which pairs the RIM-116 Rolling Airframe Missile with sensors based on the Phalanx.
These rounds are a bit more expensive each than a laser shot, and a barrage of rounds from a CIWS fires lots of rounds at some expense. Rounds fired by the Phalanx cost around $30 each and the gun typically fires 100 or more when engaging a target. The ammunition has to be stored, loaded, and resupplied. The concept of any system like this it that most of the 75 rounds per second that it fires will never hit the target. The range is limited to less than one mile of effective range (although it has a maximum range that it can lob a round of up to about three miles) and has a radar to detect income targets with a range of about 4.5 miles. It weighs about 6 tons and draws 555 volts of electric power when fully operational. It isn't cheap either at about $12 million each for the system, before considering the ammunition (fully loaded it carries 1,550 rounds) or its power and transportation demands. It is also only effective against targets traveling at up to about Mach 2, so it can't defeat a hypersonic missile.
A much smaller and more precise version of the same concept is the Israeli Trophy system, an 1810 pound system used on armored vehicles like tanks (a lighter 1,080 pound version exists as well) that has a combination of "soft kill" electronic warfare defenses and "hard kill" explosively formed penetrators (basically anti-missile bullets) along with, like the CIWS, an automated targeting system. The system costs about 30% of the cost of a new Israel main battle tank.
Trophy (Israel Defense Forces designation מעיל רוח, lit. "Windbreaker") is a protection system for military armored vehicles. It is termed an active protection system (APS) and is designed by Rafael Advanced Defense Systems.It is designed to supplement the standard armor of light and heavy armored fighting vehicles. The system is in active use on Merkava Mark 3 & 4 tanks and the Namer armored personnel carrier (APC). It is also found on the Abrams M1A1/2 tanks, and has been tested on Stryker APCs and Bradley Fighting Vehicles.The Trophy system protects against a wide variety of anti-tank threats, while also enhancing the vehicle's ability to identify enemy locations.
Trophy is quite effective against anti-tank missiles (although not perfect), and has been used with success against them since the year 2011, but not so effective against "kinetic energy anti-tank weapons" (basically fast moving tank rounds with no internal explosives and railgun rounds). As explained at the kinetic energy link:
Critics have liked Trophy to “a shotgun blast. It’s not,” the Rafael official insisted. “It’s a sniper shot…. a small number of EFPs in a very small area, aimed at a specific point on the warhead itself.” Rather than just blow the threat out of the air, Trophy tries to disable the threat so it doesn’t detonate.
It also has other vulnerabilities:
The system utilizes small EFPs which are projected towards the incoming threat; energy, debris and explosive pressure waves disintegrate the incoming projectile. As such, the system has a risk to dismounted infantry, and this system impacts traditional infantry supported mechanized warfare tactics.The Trophy system have a donut-hole like window of vulnerability to attacks from directly above, or the slow speed of the drone and the gravity-dropped grenade might have caused it to be filtered out by the Trophy’s sensors. In October 2023, Hamas used civilian DJI and Autel quadcopter drones, which dropped shaped-charge grenades to damage several tanks.
Firing multiple rounds in quick succession is also a tactic for overwhelming this system. In October 2023, Hezbollah used AT-14 Kornet missiles during engagements with Israeli forces after the onset of the 2023 Israel-Hamas War. The missiles were used from the Tharallah Twin ATGM system, which is a quadripod equipped with two Kornets fired in rapid succession. This arrangement is designed to overwhelm the Trophy APS of Merkava tanks by having a second missile available before the APS can react after the first intercept (reloading requires at least 1.5 seconds).
The Trophy system protects only a single vehicle sized target, that needs some armor to protect it from shrapnel from the intercepted incoming ordinance, and operates only at a quite short range against subsonic targets. The EPFs used by the Trophy system are presumably similar to or less expensive than tank shells.
Whether heavy passive armor beyond what is necessary to stop small arms, shrapnel (including active defense system related shrapnel), and perhaps canon rounds up to about 40 mm really adds much value in questionable.
Interceptor Missiles
A third kind of "hard" active defense system is a guided interceptor missile. Most modern warships have something of this kind, which is basically an anti-aircraft missile optimized for incoming anti-ship missiles. The are potent, effective, have long ranges in many cases, and are very expensive. And, while some of the cost is basically amortization R&D and intellectual property costs, the price of the oldest interceptor missiles suggest that the prices will remain high long after all of their relevant patents expire.
The U.S. Patriot Missile system, the Israel Iron Dome system, and some Russian and Soviet-era anti-aircraft missiles are in this category.
The size and range of these missiles vary considerably, but they tend to be smaller than anti-ship missiles, surface to surface missiles, and air to ground missiles. They generally have longer range than lasers, directed energy weapons, or slug throwing guns, sometimes much longer. They can be fired from aircraft, ships, submarines, or ground launchers (often mobile ones). They are generally supersonic and have sophisticated guidance systems. At their best, as demonstrated in recent conflicts in Ukraine and the Middle East, they can be close to 99% effective at stopping relatively large and slow moving incoming ballistic missiles and cruise missiles and kamikaze drones. But these missiles are very expensive ($100,000 to $1,000,000+ each), often the total radar and launch system is quite large.
For example, the U.S. Patriot Missile system cost the U.S. $1.09 billion each as of 2022 (foreign buyers pay up to $2.5 billion each), plus $4 million per missile (up to $10 million each for foreign buyers). It has a 99 mile range and its missiles are hypersonic (3,500-3,830 mph depending on the missile). It entered service in 1984 and has been used in ten different wars (all of which, except the Ukraine War, were in the Middle East). Each missile is up to 2,000 pounds and a C-17 can carry just one of them (which takes about an hour to set up once off-loaded). A full system with six launchers requires about 600 soldiers to support it, although each launcher can be operated by just 3 people once it is set up, loaded and ready to go.
U.S. Navy surface combatants such as Arleigh Burke-class destroyers use a variety of anti-air interceptor missiles such as the:
- RIM-66M surface-to-air missile (1558 pounds, 45-100 mile range, Mach 3.5, $238,000 each, entered service 1967)
- RIM-156 surface-to-air missile (2980 pounds, 70-150 mile range, Mach 3.5, $409,000 each, entered service 1999 with prior version entering service in 1981)
- RIM-174A standard ERAM (3330 pounds, 150 mile range against aircraft, 300 mile range against land targets, Mach 3.5, $319,000 each, entered service 2013).
- RIM-161 anti-ballistic missile (1.5 tons, up to 720 mile range, Mach 13.2, $12 million each, entered service 2014)
- SeaRAM (195 pounds with a six ton launcher which carries a 21 missile load, 5.6 mile range, greater than Mach 2, $905,000 each, relies on sensors for other weapons systems, entered service in 1992)
- AIM-120C/D or AIM-120A/B AMRAAM (356 pounds, 110 mile range, Mach 4, $1,090,000 each, entered service in 1991),
- AIM-9M/X Sidewinder (188 pounds, 22 mile range, Mach 2.5+, $400,000 each, entered service in 1956).