An explanation of how missile decoys and (missile) interceptors work, and how to make them effectively.
#Missile Decoy and (Missile) Interceptor guide
knotty haven
Missile Decoys
Missiles themselves prioritize the target with the largest detection signature of the same type the sensor head they're using can see (ie heat seekers (IR) go for the hottest target), although the detection signature is perceived to be smaller based on the missile's distance, and how many degrees the missile would have turn to point at it.
They will also go for areas of their chosen target that are the most detectable to that type of sensor head, such as as IR going for engines (fuel, steam, etc) and hot propulsion systems, or sonar seekers going for propellers, but that is only after they've picked a target (you can see where hot things are contributing to IR detection by pressing V when near a craft or building on it and checking the Heat tab).
This means that in order to create a missile decoy ("a decoy made from a missile/a missile used for decoys") that will work, the missile has to create a bigger detection signature to the missile than anything else the missile can see or otherwise might have as a target, but still be detected by the missile's seeker head.
Missiles can have decoy modules (ie Sticky Flare, Sonar Target Simulator, etc) in them instead of warheads or other offensive payloads that will create a detection signature. The more of these modules a missile has the greater the detection signature it will have, and these same modules are stronger in bigger classes of missiles (ie L>M>S). However, swarms of missile decoys don't work because each missile is considered a single target, unlike multiple hot areas of a craft.
Therefore, a single medium (or larger size class) missile is what you should be using to build a missile decoy, and filled with lots of decoy modules (of the same type), and without a thruster or torpedo propeller (we can have an ejector on the launch pad to push it away from the craft if needed). This is sometimes called a "Distraction Stick".
HOWEVER, because the guidance from missile seeker heads will reduce the perceived detection signature of any given decoy (missile based or not) to somewhere between 100% and 10% (ie anywhere from the listed value in the missile config screen down to 10% of such, the percent value that it picks is random), or 40% and 4% for missiles with signal processors, the missile decoy will need have enough of a detection signature that's at least 10x your vehicle's maximum detection range in any given direction to be guaranteed to fool missiles without a signal processor, or at least 25x for those with one.
This will require you to know how much of a detection signature your craft has, which is visible if you look in a direction while certain view mode options in build mode are active. Go by the biggest value it gives for a specific type of detection (ie IR might be 1500 but radar only 500), regardless of which direction that you look, and have your craft & engines going at whatever speed/state you expect it to be in combat when you check it's detection range or else your distraction stick might not be effective.
That said, with this setup it will simply drop the missile decoy wherever the craft is currently it's at, which may cause enemy missiles to ether miss or destroy the missile decoy, at which point they're probably going to retarget your vehicle as it has continued moving away unlike the missile decoy, therefore keeping it in the missile's sensor angle.
Now if you instead have the decoy towed behind your craft, it will significantly improve the distraction stick's effectiveness because if the missiles target the decoy but fail to hit it, even it's briefly after the decoy's destruction, they will have likely overshot the towing vehicle, likely resulting in the craft being in the missile's blind spot (unless it's radar seeking which has no blind spot).
You can do such yourself by additionally having a harpoon module on the end of the missile, (where the thruster/torp prop would normally be) and a winch block connected the missile's launchpad. You will need to then adjust the length of the cable in the harpoon module to however far back you want it to be pulled, and to disable the winch's "break at max length" setting. Ignore other settings in the winch for this as those are for pulling vehicles closer via missiles, not towing a missile behind.
If you're towing radar/IR decoys on a ship, you may want to add a variable thruster and fuel tank to the end so they avoid falling in the water, as radar/IR detection doesn't work on below water targets (meaning the missiles radar/IR seekers cannot see anything below water). For sonar decoys you do need them in the water, and therefore you may instead want a ballast tank for them to avoid reaching the surface
Three more important things to note about missile decoys/distraction sticks: Missiles with Signal Processor modules will reduce the percieved detection signature of decoys (any kind) to 40% before the guidance does the random severity reduction to any given decoy, but for campaign/adventure craft these are intentionally put only in higher difficulty craft/missiles, so it's a good idea to not exclusively rely on such when dealing with those kind of targets. Missiles using Remote Guidance will completely ignore missile decoys as they're using the AI's selected aimpoint and/or target prioritzation algorythm for their target selection. Using (missile) decoys is considered a "soft-kill" method of active defense as it only diverts missiles, and doesn't outright destroy them (like "hard-kill" methods do).
Overall, missile decoys are extremely efficient for missile defense in terms of both space and cost, but unfortunately they don't always work.
(Missile) Interceptors
(Missile) Interceptors are missiles that, instead of targeting enemy craft, will try to collide with and destroy both hostile missiles and/or CRAM projectiles (and therefore are a type of "hard-kill" system) depending on the chosen setting. They are very effective at destroying groups of small and medium missiles while still being able to inflict heavy damage on any larger missiles, while also providing some defense against CRAM projectiles (although a CIWS is far more effective for dealing with CRAMs), and do so with a minimal amount of space.
Constructing interceptors is rather simple, and is best done with small missiles, although mediums are significantly better at dealing with large missiles or CRAM, but are also similarly worse for anything less than that due to excessive overkill. Unlike normal missiles which are generally better the longer they are (to a degree), interceptors only need four modules to work at peak effectiveness, and nothing more. Interceptor Head, APN guidance, Fins, and a Variable Thruster is all that is required.
The Interceptor Head module contains both an anti-missile payload and the sensor module to target missiles and CRAMs, and even has a proxy detonation unlike other missiles once it gets really close to it's target. Said explosion from the Interceptor Head only damages projectiles (nor does it actually create fragments like the description says, it's just an explosion with a damage multiplier), so don't bother with using it for anything else.
Make sure to have the missile's internal volume to be set to fuel, and to adjust the thrust out so it has enough thrust duration to be just barely under the missile's lifespan (you can do this by clicking on the thruster/propeller module). Also make sure to set the default guidance direction to be Straight, or else it will waste some time not steering toward a target after launch. You will still need a Stagger Fire to set the stagger fire to an approximate number to space the missiles out while still firing fast enough to destroy their intended target before it hits your craft. (you DO NOT need an IFF block, but may be useful to have them avoid being shot by your own LAMS)
If you are instead dealing with torpedoes rather than missiles, simply change the thruster to a torpedo propeller, as thrusters don't work in or under water. While torpedo propellers move missiles much slower than thrusters, they're also much more fuel efficient, in addition to doubling the missile's normal lifespan. Therefore fuel consumption/duration will need to be different than with thrusters.
However, there are two major design traps with building interceptors that you should know about and avoid.
Adding some extra HE or frag warheads to deal more damage to enemy missiles is a complete waste as the interceptor head itself deals so much more damage than any of the payloads that it completely overshadows any extra damage to be gained by a longer missile. If, by some reason you were to do such (and I strongly advise against it), use very low angle frag (ie 10 or so), but please do not use more than 4 modules.
Another trap with designing interceptors, is making them long enough to have a secondary torpedo propeller in addition to a thruster. This will usually cause them to mostly go after a single torpedo that is fairly close or a CRAM that has sunk into the water and no longer poses a threat, while ignoring a group of several missiles that are much farther away and would be far more destructive.
Automating Their Deployment
Setting up the automatic launch and deployment of both Missile Decoys and (Missile) Interceptors is fairly simple and entirely identical.
Place an ACB (Automatic Control Block) as close to the missile controller as you feasibly can, directly touching it even. Then set the ACB's triggering condition to be enemy missiles within a given desired distance. 2000m is ideal for an absolute maximum trigger range, as that is generally the longest a missile can travel before expiring (factoring in some loss for not moving in a straight line toward it's target that is), but you may desire to reduce this to about 1600m. The longer the distance it checks, the more time your interceptors have to start launching and get to the incoming missiles before they hit your vehicle, and making it too short will increase the likelihood of getting hit by enemy missiles.
Make sure to adjust which combination of missiles and/or torpedoes it triggers on, or else you may have torpedoes trigger your missile interceptors, only for them to be wasted if there's no projectiles above water or vice versa.
For the action it takes when it triggers, set it to fire weapons systems, and limit the distance it can control blocks to be as small as possible while still including the missile controller itself. The farther the ACB is from the component we want it to control, the greater the possibility that some other weapon system is also the same distance from the ACB and will be triggered as well.
Last but not least, you will need to have Munition Warners (which are in the defense tab of the build menu) or other forms of detection on your craft that can see projectiles, or else the ACB has no way to know there are missiles the first place. For underwater projectiles you will instead need a sonar detector as most forms of detection cannot see underwater at all (which is why submersibles are so sneaky).
Guide End
vernal tendon
One thing missing here that no one seems to know. How long does the effect of decoys last?
sullen temple
One thing missing here that no one seems to know. How long does the effect of de...
Until the missile is destroyed...?
loud root
this tutorial could also include use of interceptors with ciws controllers to reduce missile overkill and coordinate multiple turrets
hidden oasis
Until the missile is destroyed...?
Flares have a set amount of time I recall
hidden oasis
One thing missing here that no one seems to know. How long does the effect of de...
Flares have a set amount of time, click on the module and adjust the setting as you wish
Max was 15 seconds I recall
sullen temple
Wasn't it proven that the visual effect doesn't represent the decoy strength?
sullen temple
Max was 15 seconds I recall
The only slider on the flare is when you want them to activate and when you want them to drop 🤔
hidden oasis
The drop part is the important thing I recall
After it drops the flares stop working
This is what I recall last time I tested
Gonna check the log, wait a moment
sullen temple
The drop is just a little gimick though, you shouldn't use it as the decoy (It drops each decoy module individually so you lose all your decoy strength)
hidden oasis
Hmm, does the flare drop time change depending on the missile size?
Since checking the log the default for the flare drop time is 20 seconds it seems like. Meaning the flares stop working after that
The log was on 1/3/2023
sullen temple
It doesn't change no
hidden oasis
Will check ingame after I come back home though
If it doesn't change then the max time of flares would be 20 seconds wouldn't it be?
Since it drops at that time
sullen temple
Ok yea, confirming that there is a max 20 sec time on flares (On the missile itself)