Decoy Missiles
Decoy Missiles are designed and produced in the same way as missiles. To design a decoy missile, click the Decoy Missile checkbox on the Missile Design window and enter “Decoy Strength”, which is an MSP value and a replacement for warhead strength. This is the only field that matters for Decoy Missiles and the size of the Decoy Missile will be equal to the “Decoy Strength”. The decoy missile also has an ECM value equal to the current Missile ECM technology.
The minimum size of a Decoy Missile is 5 MSP.
The Decoy Missile has a ‘Signature’ equal to its MSP * 200 tons. So a size 10 Decoy Missile would have a signature of 2000 tons. The cost of a Decoy Missile is equal to MSP * 4 BP, so a size 25 Decoy Missile would have a signature of 5000 tons and cost 100 BP. The entire cost is in Corbomite.
Decoy Missiles are launched from Decoy Launchers. These are similar to box launchers, although 1/3rd smaller for the same missile size. They are not reloadable outside a hangar. For example, a size 25 Decoy Missile would require a launcher of 2.5 HS (125 tons).
Decoy Missiles can be assigned to Decoy Launchers on the Ship Combat tab, using the normal drag and drop functionality. All Decoy Launchers are listed in their own section on the Combat View and are not linked to fire controls.
During missile movement, after point defence fire but before CIWS fire, each ship will make its own determination as to whether to launch one or more Decoy Missiles. This is based on the Decoy Threshold, which is set on the Combat View by clicking a button and entering the value. The default is 100. I will also add some functionality around a Class Decoy Threshold, that will apply as a starting Decoy Threshold for new members of that class, or be used to update all members.
If the total MSP of inbound missiles targeted on the ship is equal to or greater than the Decoy Threshold, at least one Decoy Missile will be launched. The total number of Decoy Missiles launched is equal to: Round Down (Total Inbound MSP / Decoy Threshold). If there are different types of Decoy Missiles assigned to available Decoy Launchers they will be launched in order of descending size, then order of descending ECM rating.
Any missiles that survive CIWS and successfully roll their Chance to Hit will be checked to see if they hit the Ship or one of the Decoy Missiles. The chance to hit the ship is equal to: Size Ship in Tons / (Ship Size in Tons + Total Signature of All Decoys). Multiple warhead missiles will check each warhead independently.
If an attacking salvo has ECCM greater than the ECM of the Decoy Missiles, the signature of each Decoy Missile will be equal to: Decoy Signature * (1 - ((ECCM - ECM) * 0.2)).
At the end of the missile movement phase, all Decoy Missiles will be removed.
NPRs will design ships with Decoy Missiles.
N.B.I played around with many different mechanics and UI options before deciding on the above. One option I almost implemented was a decoy missile with endurance that followed a ship until destroyed. However, that added a lot of micromanagement in terms of deploying the missiles and would also encourage a swarm of smaller missiles rather than a single, more manageable large decoy. It would also be a lot harder for the AI to make sensible decisions with those mechanics. Further to that, any persistent decoy mechanics, even with instant launch, led to similar issues around decoy swarms. I also considered manually triggering decoy missiles prior to missile movement, but that would also require micromanagement and would require information on which inbound missiles were targeting each ship. Eventually, I decided an automated chaff-style system would be the easiest to manage for both the player and the AI, while giving the player some flexibility to adapt to different situations by changing thresholds.