Naval Weapons

The weapons you find on warships and submarines. Not stuff that fires out of your belly button.

Anti-Air

Air attack has been a big potential issue for warships since before the Second World War, a war that of course saw Pearl Harbor. These days, the primary manifestation of this threat is the anti-shipping missile, launched from an aircraft, ship, submarine or a shore-based battery. You can shoot these down, or preferably, blow up the guy with the missiles before he launches them, and anti-air weapons are good for both.

Historically, the main determinants of AA effectiveness have been fire control- the ability of your radars to track enough targets, how fast you can fire your guns/get your missiles off, and how likely they are to hit their targets.

SAMs

A Surface-to-Air Missile (SAM) is a missile which is launched from a surface platform and attacks an aircraft or missile. Invented in the 1950's, they vary from short-ranged, barely guided early models to modern missiles capable of hitting other missiles in mid air and doing so from hundreds of miles away from the launching ship. Unlike their air-to-air counterparts, naval SAMs generally use a command-guidance or semi-active homing scheme; that is, the launching ship either guides the missile the entire way to the target or illuminates the target with a radar beam, the reflection of which the missile homes in on.

Considering the self-guiding, "fire and forget" ability of modern missile technology, this seems an anachronism but confers several advantages: by shifting the processing power to the launching ship, the missiles can take advantage of bigger computers, can have more warhead or fuel for the same size missile, and are cheaper, with the same guidance capability. Since the ship can usually point its radars in any direction, following the target is not a problem, either.

Older naval SAMs used rail-based launchers or box launchers. Rail launchers usually had one or two missiles sitting on rails, basically providing you with one or two missiles available to launch before the launcher would reload from an automated magazine below decks. A box system came with say eight missiles in a launcher out on deck which you would then have to reload manually. These looked visually impressive, but caused a rate-of-fire issue. Either you could fire one or two missiles, and then spend 30 seconds to 2 minutes reloading, or fire eight missiles, and then spend 45 mintues reloading.

Today, the Vertical Launch System (VLS) is generally used, with missiles placed in silos inside the hull and launched on command. This is basically a box system with a much higher ammo capacity: it allows you to get a missile off about once a second (or faster), lets you carry bigger missiles, is mechanically much more simple and reliable than the automated reloading and aiming systems associated with rail and box launchers, and reduces your radar cross-section (making you harder to find and hit).

However, isn't easy (or sometimes not even possible) to reload at sea without an ammo ship and special crane. Your launch-to-impact time is also slightly slower, because with a rail or box system, the missile is already pointing at the target when it fires, whereas in a vertical launch system, the missile has to launch and then turn towards its victim. Modern naval SAMs generally compensate for this by Roboteching, some turning from vertical to horizontal flight so fast that they barely clear the railings on the side of the ship on their way out.

Area defence surface-to-air missiles

Missiles with a range in excess of 10 nautical miles, used to defend multiple warships. Usually found on destroyers and a job requirement for cruisers. Most are designed to hit incoming missiles and find regular aircraft laughably easy targets.

The US Standard series, especially linked in with the Aegis system that allows for dozens of targets to be engaged simultaneously and for sharing of targeting information.
The Soviet/Russian S-300/SA-N-6 "Grumble" and its successors.
The British Sea Dart system.

Point defence surface-to-air missiles

Found on most smaller ships and also ships like carriers which have no other air-defense systems. These are generally very short-range and are installed as a last ditch effort to save the ship from being hit by missiles that the area-defense weapons miss. These sacrifice range and explosive power for for speed and accuracy, and unlike CIWS systems have the ability to engage multiple targets simultaneously. Many of these still use box systems so that they can be installed on a variety of different ship types, and because keeping the time from launch to impact short is of deadly importance.

The US RIM-162 Evolved Sea Sparrow. These are fired from deck-mounted box launchers or from a VLS.
The RIM-116 Rolling Airframe missile, which was jointly designed by the US, Turkish, Hellenic, German, Egyptian, and South Korean navies as a replacement for the PHALANX CIWS. 13 or 21 can be carried in a box launcher.
The Soviet Osa/SA-N-4 "Gecko", found mounted on a wide variety of their ships.
The French Crotale eight-tube system.

AA guns

During WWII these were the primary anti-aircraft weapons, but were rendered obsolete by the combination of carrier aircraft, long range missiles, point defense missiles and CIWS. These are still in limited use for defense against "low-slow fliers" like helicopters or hypothetical small kamikaze aircraft flown by terrorists.

The Browning M2 .50 caliber Heavy Machine Gun was originally designed as an anti-aircraft weapon, and may still be used as such for slower, closer-in targets.
The US Mk 45 5" gun system can fire fragmentary rounds that have a radar fuse as a secondary air defense weapon, much like old-school flak.

Close-In Weapons Systems (CIWS)

Separately from or in cooperation with point defense missiles, these are radar-aimed gun systems designed as a last-ditch defense against incoming missiles. They are typically highly accurate and have absurdly high rates of fire; with the drawback of short range-even if you do score a hit, momentum will probably still carry the fragments of the incoming missile into the ship. Their ammo consumption is also generally so ludicrously high that even firing in bursts you may run out of ammo even well before a point-defense missile system would.

They're also rather good at shooting up empty pirate skiffs.

The US PHALANX system uses two radars and a 20mm gatling gun; due to its appearance often referred to by sailors as R2-D2 with a hard-on.
The Dutch Goalkeeper system.

Carrier-based aircraft

While not necessarily a weapon in and of themselves, the outer ring of air defense for a sufficently large strike group will be formed by the carrier's air wing. Airborne early warning aircraft extend the radar horizion and fighters can visually identify and engage hostile aircraft, or provide early target information for naval SAMs. Many fighters are also light bombers/attack aircraft and can be used versus surface ships, and helicopter squadrons provide an antisubmarine capablilty.

The F-14 Tomcat of Top Gun fame; now retired from US service with a few hanging around in Iran.
Its replacement, the F/A-18 Hornet, is a "strike fighter" which can attack surface or air targets.
The E-2C Hawkeye provides long-range radar coverage.
The SH-60 Seahawk helicopter comes in several flavors, of which the B, F, and R variants are designed for antisubmarine warfare.

Anti-surface

The original form of naval warfare. As with air defense, carrier-based aircraft can also help perform this role.

Anti-shipping missiles

These are typically the nastiest surface-to-surface threats out there. Also known as Anti-Ship Cruise Missiles (ASCM), they can be launched by aircraft, submarines, ships, or land-based launchers, fly more than 100 miles at extremely low altitude, accelerate to supersonic speed, weave to evade interception, and then impact the target with enough explosives to blow some smaller ships in half.

They generally come in two types. The first, as described above, are called sea-skimmers. They fly a few feet above the waves to make detecting them on radar extremely difficult, usually at subsonic speeds to extend range. Newer ones are capable of evasion, and some can be programed to fly a roundabout path to the target to hide where it came from. This is so terrifying for defending units because the low altitude reduces the amount of time to react (a minute or less). Even the best air defense missiles take time to reach the target...and the incoming missile may take less time than that to impact.

Example:

The U.S. Harpoon
The French Exocet, infamous for its high performance in The Falklands War and Iran-Iraq War.
The Russian 3M-54 Klub/SS-N-27 "Sizzler"

The second type are missiles that fly extremely high and extremely fast, and then dive down onto the target. These are less common today because advances in SAMs mean that despite their speed, their high altitude means that shipboard radars can track them almost their entire flight, giving numerous chances for defenses to engage them. Their one advantage today is that they can typically carry a larger warhead. Some Soviet missiles of this type had one missile in the salvo one would fly up to and use its active radar to search for targets, forwarding this data to the other missiles which remained at low altitude. The missiles could be programmed so that half of a salvo would head for a carrier target, with the rest dividing between other ships. If the high flying missile was shot down another from the salvo would automatically pop up to take its place.

Example:

The Russian P-500 Bazalt/SS-N-12 "Sandbox"

Main guns

The oldest form of surface weapon, and consequently usually the most reliable. Modern guns are typically of lower caliber (3" to 5") than their predecessors from before WWII (12" to 18") but because of the overwhelming power of the missiles refered to above, most modern ships are not particularly heavily armored. Naval architects reason that a direct hit by an ASCM would be game over anyway; instead they use the space for more self-defense weaponry. Thus smaller shells will do just fine.

Modern guns are usually largely automated, aimed by radar, and have a rate of fire between 20 and 80 rounds per minute, a significant improvement over older weapons that required large crews, were aimed optically, and had slow rates of fire. Range is typically out to the visible horizon, some 10-15 miles. Some can be loaded with specialty ammunition for use against different threats, though the standard High Explosive is the most common and most useful. They may not be as powerful as missiles but they will get the job done cheaper, more reliably, and at close range, faster.

A note about the term "caliber": when talking about small arms (pistols, rifles, machine guns, etc) caliber simply refers to the diameter of gun's bore (and thus the width of the bullet). When talking about Naval guns, caliber refers to the ratio of the width of the gun's bore to the gun's length. In other words, a 16"/50 caliber weapon, like the ones carried by the old Iowa class battleships, has bore that's 16" wide and a barrel that's 16 x 50 = 800" (66 2/3 feet!) long.

The US Mk 45 5"/54 caliber "lightweight" gun (and the 62 caliber version)
The OTO-Melara 76mm/62 caliber gun is used as a smaller but rapid firing gun used by a number of navies, including the US FFGs and several of the US Coast Guard's cutters.

Machine guns

Exactly What It Says on the Tin. Smaller-caliber, rapid firing. Machine guns mounted on ships have several advantages over their land-based bretheren: The ship itself provides a stable firing platform, an armored position to fight from, and storage space for literally tons of ammuntion. They provide defense against fast-moving small vessels, and in port against personnel on foot and in vehicles. When mounted in small, fast moving boats, they become the primary armament. Although there are exceptions, they are generally not automated and instead operated by crewmembers.

The US M2 .50 cal heavy machine gun. You can use it for anything. If you could find a way to get rid of the water in between, you could probably sink submarines with it.
The US M240B 7.62mm medium machine gun
The US Mk 38 is a 25mm chain-gun that comes in two varieties: The manually-opearted Mod 1 requires a sailor to stand out on deck to aim and fire it, while the Mod 2 is remotely controlled and aimed by video camera. Both need sailors standing by with extra ammo to reload it with.
The Russian PKM medium machine gun.

Sailors

Navies have been individually arming sailors since navies were invented. During the Age of Sail, boarding actions carried out by crewman with axes, cutlasses, and pistols were an important means of winning battles. While the invention of accurate long-range guns ended the days of daring boarding actions, most ships have a team of specially-trained sailors for boarding (ostensibly) unarmed vessels and for inport security. Boarding teams are usually at least as well-armed as the average infantryman on land and will typically have nifty things like ballistic vests that are also flotation devices, rope ladders with hooks and poles for getting up the side of ships, and tools for cutting through metal doors. Their weapons are generally more compact so as to be easier to manuver inside cramped ships.

Heavyweight Torpedoes

Essentially self-propelled underwater bombs, modern torpedoes have evolved quite a bit from the straight-running, short ranged weapons seen in World War I and World War II. The modern varieties come in two general types; heavyweight and lightweight. Heavyweight torpedoes are only carried by submarines, and can target subs or surface ships, while lightweight torpedoes are launched by aircraft and ships, but can only target submarines. We'll leave the lightweights for the anti-submarine section.

Heavyweight anti-ship torpedoes are truly fearsome weapons. Most have ranges in the dozens of miles, they can move at double the max speed of most ships and submarines, and due to their large size have bigger warheads than any other naval weapon (excluding nukes, of course--though there are nuclear-tipped torpedoes); many are capable of blowing cruiser-sized vessels clean in half. Newer ones also have multiple guidance methods; they can be quietly guided by wires from the launching sub until a certain distance, but then use acoustic seekers, and their detonators can be magnetic. They are also very difficult to decoy.

The US Mk 48 ADCAP heavyweight torpedo is the very latest long-range, surprise underwater demolition equipment. It's also used by the Canadian, Australian, and Dutch navies.
The British Spearfish is a comprable weapon.
The Chinese Yu-6.

Anti-submarine

This is without a doubt the hardest surface warfare area. You can never actually see your opponent; his sensors are probably better than yours, and he is in a better position to hear you than vice-versa. He will be carrying superior torpedoes, and while you have to train to defeat aircraft, surface ships, submarines, ballistic missiles, launch and land your own aircraft, and strike at ground targets, he only has to train against ships and subs. If he's a diesel-electric, he wont' be able to go very fast or stay down forever, but he will be almost totally silent. If he's nuclear-powered, he will be slightly louder but he will be faster than you (!) and be able to stay down for months. As a surface ship your only advantage will be your ability to call for friends, ideally aircraft, because he can't shoot back at them, while he can't communicate with anyone without giving away his position.

On the other hand, anti-submarine warfare conducted by subs is essentially an equal playing field, with the winner determined by a combination of equipment and skill (training).

Lightweight Torpedoes

While the heavyweight behemoths described above can also catch and destroy submarines (and are very good at it) they are typically too large and heavy to be carried by aircraft, and take up unnecessary space on surface ships. Lightweight torpedoes are about 1/3 as heavy and are still deadly weapons. They take a "just enough" approach to destroying submarines: they are shorter-ranged than heavyweights; they won't blow one in half, but instead are designed to cause a sufficiently large explosion sufficiently close to the submarine to crack its pressure hull, burst pipes, blind its sonar, and otherwise cause chaos within. Helicopters can usually carry two or three of these, surface ships these days usually have four to six of these ready to go (with plenty of extras in the magazines), and maritime patrol aircraft can carry sometimes as many as eight.

The US Mk 46 Mod 5 is a refinement of a design that has been around since the 60's.
The US Mk 54 is its intended replacement.

Depth charges

A depth charge is a bomb that is dropped in the water and set to detonate at a certain depth; either by pressure or by a timer. Their advantages are that they are cheap and simple to operate; their disadvantages are that they are very short ranged and unlike torpedoes, will not follow their targets around until they hit them. For this reason, depth charges were very common in World War I and World War II but almost no navies carry them today. Like lightweight torpedoes, these are not designed or intended for direct hits; near misses would be good enough.

Mines

The reason why we have Minesweepers. Mines, like their land-based brethren, are bombs that sit inert until they are triggered by some external stimulus. There are literally hundreds of types of mines, and they are all deadly. Any seagoing vessel or aircraft can be a minelayer, and all ships and submarines are vulnerable. The best ways to categorize them are:

Position in the water
- Free-floating
- Moored at some fixed depth from the bottom
- Resting on the bottom
- Buried under the bottom
Detonation mechanism
- Contact (something touches the mine)
- Acoustic (the sound of a specific ship)
- Magnetic (the magnetic signature of a metal hull)
- Pressure (the pressure of a ship or sub passing over them)
- Timed (the mine detonates when its timer runs out)
- Command (whoever laid the mine sends a signal to detonate)

The most insidious mines use a combination of the above; for example, there are mines that sit on the bottom, listen acoustically for a certain ship type, and then only float to the surface after a certain number have passed by, and only detonate when it gets the right magnetic signature to be sure it is close enough. Many navies try not to use mines if they can help it because they hate them and don't want to give their enemies any bright ideas.

Stand-off antisubmarine weapons

These are usually rocket-thrown torpedoes of some sort. A rocket or a missile carries a lightweight torpedo or depth charge out some distance from the launching ship, and then drops it into the water, where it activates and acts like a normal torpedo or depth charge. Some are simply ballistic (rocket flies in an arc, drops torpedo) while others are guided. This is a good way for a surface ship to keep itself away from a sub, but still no substitute for having anti-sub aircraft around. The one exception to this is when the "depth charge" carried by the rocket is actually a Nuclear Depth Bomb, in which case it will take out every submarine within a two mile radius or so of the impact point.

The US ASROC (AntiSubmarineROCket) and its successor, the Vertically Launched ASROC (VLA). Basically a Mk 46 torpedo with a rocket attached. The ASROC could also carry a Nuclear Depth Bomb in case the ship ran into serious submarine trouble.
The Australian Ikara

Sonobouys

Sonobouys are not strictly weapons per se but are still an important part of hunting submarines. They are basically bouys with small sonar systems hanging underneath them, underwater, that can be launched by aircraft or thrown over the side by surface ships. The acoustic data they gather is then transmitted back to the parent ship or aircraft, effectively providing the originator with the ability to listen in more than one place at the same time.

Land attack

This role has been attempted by ships since cannons were invented but it only became truly effective in the 19th century. Before that, fortresses on land could could mount larger, longer-ranged guns than ships could, and even the largest shipboard guns couldn't penetrate thick fortress walls. Firing indirectly (in a high ballistic arc) was too inaccurate to reliably accomplish anything. However, the invention of explosive shells, stabilization and fire control systems, and later missiles, enabled ships to become convenient floating artillery batteries. Land attack can be used in a fire support role for ground troops (perhaps for an amphibious assault), for aircraft (Suppression of Enemy Air Defenses or SEAD), or to strike specific strategic targets.

Main Guns

Once again, main guns were the original form of shore bombardment. Naval guns are usually highly automated, or at least mechanized, so their firing rate is much higher than field guns of similar caliber, which have to be light enough to be dragged around by trucks. One ship can provide nearly the same amount of shells on target at a time as an entire battery of field artillery. Their main limitation is typically range; The ship can only get as close to shore as its draft allows, and max range is usually around 10-15 miles. When the marines push farther inland than that, they're on their own.

The Mk 45 5" gun mounted on US CGs and DDGs fires at a rate about 20 rounds per minute, or one every 3 seconds. If that wasn't impressive enough, CGs have two, and by alternating fire they can put a round on target once every 1.5 seconds. Marine spotters love this fact.
Though there are none in active service today, the all-big-gun battleships of the 1900s to 1940s were perhaps the most fearsome naval fire support platforms ever. Their heavy armor meant that they could take fire from land-based guns and ask for more, and they typically mounted upwards of 9 very heavy caliber guns. The US Iowa class ships mounted 9 16"/50 caliber guns which they could fire about every 30 seconds, independently. This means either a full broadside of 9 rounds every thirty seconds or a rolling fire of 1 round every 3 1/3 seconds. For an enemy soldier, this was equivalent to a Volkswagen filled with high explosives landing on your position from 20 miles away every few seconds until the Marines told them to stop! That, or 9 50-foot craters suddenly appearing at your position at once. You Can Panic Now.
- The Iowa and Wisconsin were last used during Desert Storm in 1991 to shell Iraqi positions. The Iraqis realized that UAVs (some of the first used by the US Navy) were used to spot targets for the big guns, and eventually just started surrendering when the UAV flew overhead, rather than get blown to smithereens from a ship so far away they couldn't even see her.

Cruise missiles

Cruise missiles are flying, self-guided bombs. Many are closer to small unmanned aircraft filled with explosives than they are to regular missiles, being jet-propelled rather than rocket-propelled. They were first invented in World War I, but the earliest versions to see action were the German V-1 missiles in World War II. Some nations forgot the unmanned part. Modern cruise missiles will usually fly slower than other types of missiles (subsonic), cruise to the target at low altitude for hundreds of miles, and then impact with "pick a window" accuracy on a target. They are able to be programmed to evade air defenses on their own, and some of these can be fitted with nuclear warheads. Ships or submarines equipped with Vertical Launch Systems can pump out dozens of these at a time. They are used to strike at strategic targets either close to shore or far inland without endangering the launching unit very much.

The most (in?)famous of these is the US Tomahawk, which can be fitted with a single warhead, cluster munitions, or a W61 nuclear warhead.

Ballistic missiles

As the name would imply, these missiles fly to their target in a ballistic arc. They are not nearly as accurate as cruise missiles but typically have much longer (intercontinental) range and response time and as such are today only carried by submarines and fitted with nuclear warheads. Each missile can be fitted with Multiple Independent Reentry Vehicles (MIRV) which are warheads that can hit several targets independently, and they can be fired while submerged. The job of SSBNs or "Boomers" are to hide until such time as they are ordered to fire these, and usually carry 1-2 dozen of them. Thankfully, none have ever been fired in anger.

The US Trident II, carried by Ohio class SSBNs.
The People's Republic of China are widely believed to be working on anti-ship ballistic missiles for use against US carrier groups.

Other things that make warships better

Electronic Warfare suites

There are whole books written on this topic, but for the purposes of this article, this is basically warships listening for enemy radars or broadcasting jamming to confuse enemy sensors. This can allow you to detect enemy ships long before they can pick you up on radar (by its very nature, to get a radar return, the signal needs to go from the transmitter to the target and back; the emitter has to have enough power to send signals double its maximum range). If your own emitters are turned off, you can then track them without needing your own radar. You can use common civilian radars to fool the enemy into thinking you are a merchant vessel. Also, EW plays a key role in defense against ASCMs; detecting the missile's radar seeker may provide you more warning than your own radars, and you may be able to jam its seeker and confuse it. Most modern combatants mount some sort of EW system.

Ballistic Missile Defense

Modern ballistic missiles are basically every defense planner's worst nightmare: they can be launched with little-to-no warning, fly hundreds-to-thousands of miles in a matter of minutes, and then deliver multiple nuclear weapons to different targets anywhere on the globe. Worse yet, it's impossible to know exactly where they're aimed at until they fire, at which point it is too late to move defensive assets into the path of the missile.

That last one is why in many ways, ships are ideal Ballistic Missile Defense (BMD) platforms. Thanks to international waters, they can move anywhere there's ocean, and unlike aircraft, they can loiter in good intercept position for months without requiring a base to return to.

To understand BMD, you need to know a little bit about how Ballistic Missiles operate. There are three phase of flight: Boost, Midcourse, and Terminal.

In the Boost phase, the missile is taking off from its launcher and its rocket motor(s) is/are burning. It takes about 5-10 minutes depending on the range to target. The huge, hot exhaust plume makes it easy to detect and track, and it's at its most fragile during the stresses of acceleration. Unfortunately, to intercept a missile in boost phase, you need to be relatively close to the launch site, have a good idea of where the missile is heading, and have an interceptor system that can catch up to and overtake a missile which is literally rocketing upward and acclerating into space. Also, unless you expect a launch, you may not have sensors looking in the right direction to detect the launch until the missile is at higher altitude.
In the Midcourse phase, the missile's motor has burned out and it is coasting on a ballistic arc towards its target. For ICBMs, this will be outside the atmosphere. During this phase the boost stages will drop off and if the missile has multiple warheads, they will separate and manuver to point towards their respective targets. Surface-based radars should be able to easily detect them now, and once they are being tracked it becomes relatively easy to figure out where they are headed. This is the longest phase, giving a defender the most chances to intecept them. The hard part about intercepting in midcourse is that most missile designers today include decoys with their warheads that make it very difficult to tell which are real warheads and hit them, and again, the warheads are moving very, very fast.
During the Terminal phase, the warheads have re-entered the atmosphere and are screaming out of sky nearly direcly on top of their targets. The decoys are now gone, slowed by the atmosphere while the denser warheads fall through. This is the shortest phase, lasting about 30-60 seconds. It ends when the warhead detonates on or above its target. The obvious disadvantage of a terminal BMD system is that you have to be near the target, and you have maybe one chance to intercept every incoming warhead before you are converted into radioactive ash. You'd better hope your missiles are fast and your aim is good.

Most ships are best suited to perform midcourse BMD, which would allow them to cover a broader area and take advantage of their existing systems To do this, a ship would need radars capable of seeing into space, missiles capable of reaching that high in a very short time, and a guidance system capable of "hitting a bullet with a bullet", as both the interceptor missile and the ballistic missile or its warheads will be moving in different directions at thousands of miles per hour.

This is a very new warfare area, so feel free to post new examples as they are invented. Or don't, if keeping such things a secret are important to you.

The US is attempting to turn its CGs and DDGs equipped with Aegis into BMD ships; it appears to be the most successful system so far.

Decoys and countermeasures

These are not so much weapons but rather things which make it harder for weapons to hit you.

Flares

Exactly What It Says on the Tin. Warships carry flare launchers to decoy IR Guided (heat-seeking) missiles by creating a heat source hotter than the ship's exhaust. Ideally, the missiles go after the flares and not the ship.

Chaff

Chaff consists of thousands of small strips of metal which are fired into the air in a "cloud" to decoy radar-guided missiles in a similar manner to flares: They create a radar target larger than the ship for the missile to home in on. The British proved that these work during The Falklands War, though they also demonstrated that you should be carefull where exactly you fire these off; in at least one case an incoming missile was fooled by the chaff launched by destroyers, flew through it, and then aquired the next target it found on the other side, which turned out to be a merchant converted into a cargo transport by the British. Whoops.

Active radar decoys

These work by flying out away from a ship and then turning on a radar repeater which imitates the signals from a radar-guided misile and hopefully causes it to belive there's a bigger ship where there actually isn't. These are generally more effective than chaff but are generally much more expensive and can get as big as small missiles, so a ship will usually have fewer of them if it has any at all.

The joint US-Austrailian built NULKA is one of these.

Acoustic decoys

These are decoys either fired underwater or towed behind a ship or submarine whose job it is to fool torpedoes into either going the wrong way or detonating early. Some are noisemakers which imitate the sound of a legitimate target, some are essentially "jammers" which flood the water with sound to confuse sonar, some form a "screen" of bubbles to try and provide active sonar with a bigger target than the submarine/surface ship, and finally some generate a magnetic field intended to fool a torpedo's detonator into thinking its found the target. Some incorporate more than one method. They vary in effectiveness.

The US AN/SLQ-25 "Nixie" is one of these.

Stealth design

One way to avoid getting hit by misiles is to avoid being detected at all. New warships are now being designed so that their radar-cross section is reduced, making it harder to detect them initially and then harder for missiles to lock on. This started in the US in the 1980s but the practice has now become commonplace around the world. Generally it involves eliminating right angles and clearing away or concealing objects sticking out on deck and on the sides of the ship. This also has the added benefit of making the ships look more sleek, deadly and futuristic without all that ungainly, random crap like radars, antennas and deck fixtures sticking out.

For an example of the progression stealth ship design has undergone, examine the shapes of four US warships from the last 30 years:
- The Spruance Class destroyers were built in the 1970s and 80s, before the advent of stealth features for ships.
- The Ticonderoga Class cruisers were originally designed without stealth design, but some features were later added to improve it, such as radar absorbent material.
- The Arleigh Burke Class destroyers were the first US ships built from the beginning to be stealthier; note the lack of prominent right angles and the major reduction of topside clutter.
- The San Antonio class amphibious assault ships represent the latest in stealth design; you can see how all most all of the antennas and protrusions topside are either missing or hidden inside the two large masts. Even the anchor is hidden from any angle a radar might see it from.
- And then we have the planned Zumwalt class destroyers. Note the even more dramatic absence of protrusions and random clutter. This design may also someday include a railgun, which will need even more clever engineering to conceal.