Talk:UFO Interception

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TBD: Discuss pursuit on the Geoscape, bad intercept vector algorithm, speed differences, etc. Also re-engaging targets, targets that land, over land vs over water, multiple interceptors.


Interception Attack Modes

[TBD Summarise. Actually the main article already summarises this well.]

I noticed recently that the different attack modes have different functions. I'll briefly summarize what I saw here, and if someone can confirm, we can add it to the wiki.

Cautious Attack: Enter range to fire with longest range weapon. Pull back to standoff distance if craft takes damage from UFO return fire.
Standard Attack: Enter range to fire with both weapons. Pull back to standoff distance if craft takes significant damage from UFO return fire [in one shot?].
Aggressive Attack: Chase UFO to get as close as possible(64 range units), firing weapons all the way. Never pull back to standoff distance.

Also, the UFO seems to have a greater chance of running away at the more cautious settings, [and vice versa] but that makes sense. ;) Arrow Quivershaft 01:29, 29 February 2008 (PST)

I'm not entirely sure what the differences in behaviour regarding pulling out into standoff range when damaged are between the various modes (hadn't really noticed it too much myself), but the modes mainly function at adjusting the range of the craft and UFO.
In short: out of firing range, longest ranged weapon, shortest range weapon and as close as possible. One note about cautious mode is that it will revert to the next closest loaded weapon. If the longest range weapon runs out of ammo, the ship will close in to the next best weapon.
It's odd we left this explanation out, but yeah it needs to be there. - NKF 02:22, 29 February 2008 (PST)

Any Interception craft at "Cautious Attack" that takes damage will attempt to retreat out of range to Standoff distance. Craft on "Standard Attack" will do the same sometimes. I see it most often when chasing Battleships with Firestorms or Avengers, and they get knocked good by a shot from the Battleship. Happens more often with Firestorms, so it's probably percentage based. Craft on "Aggressive Attack" will never return to standoff distance unless changed to a different mode or ordered to pull back or disengage; in that mode, the mentality is "Him or me."

I don't get to see this much anymore because I usually use Aggressive Attack because a lone Avenger can go toe-to-toe with a Battleship and still make it back in fairly good shape(30% damage or so). A Firestorm can usually manage to limp back as well, but in considerably worse condition. Arrow Quivershaft 12:25, 29 February 2008 (PST)

I've changed the main page to show some scepticism as to whether UFO damage vs interceptors increases due to interceptor attack mode. I don't believe it does. Spike 08:40, 16 August 2014 (PST)

Engaging with multiple craft

If I understand the latest edit, UFOs will not "divide" their fire amongst multiple targets, but will fire at each of them as frequently as they would fire at a single ship. If that's the case, is there really any advantage to having all ships engage at the same time?--Ethereal Cereal 15:29, 5 March 2007 (PST)

Thats because whoever wrote it was a moron, thats precisely what doesn't happen as I finally managed to identify just before writing it. Its tough to tell though, especially as you cant get them all to go in at once, and if you go in on aggressive attack it gets very quick at the end and hard to say whats going on. --Sfnhltb 15:43, 5 March 2007 (PST)

The most convincing aspect for me anyway was the results - three interceptors armed with plasma mostly going in singly almost always get eaten, three at once (or as close as you can get it, and setting the cycle speed way down helps synchronise them better) nearly always wins and often doesn't take a single casualty. --Sfnhltb 15:47, 5 March 2007 (PST)

From what I can remember, the UFO's rate of fire gets faster and faster the closer you get to the UFO. I've tested this with two different ships with identical armament, with one on aggressive and the other on cautious. The one on cautious fired normally, but the one that got right up to the UFO was exchanging and receiving ammo at a considerably faster rate than the one on cautious.
That still this doesn't answer the question wether the UFO splits the attacks or fires on the ships normally.
Still, I find the odds of knocking out a UFO with multiple ships a lot better than to attempt it sequentially. (edit: or mind you if I'd checked through all the edits, all this has been covered already. Oh well.) - NKF
I did 10 tests each way yesterday from the same save - sequentially 1 win from 10, even that the last interceptor was fully red damage at the end (cant tell the exact numbers, for some reason after the fight the geoscape was zooming out past maximum and crashing to the battlescape). Simultaneous was 9 wins from 10, 0 shot down 2 times, 1 down 4 times, 2 down three times. I then did a few further tries later with all three having slowed the cycle rate down and got 0 shot down 3 times out of 4, as generally the first one in was the one that almost always died if any did, if you can get them all attacking closer together it ensures it doesnt take the first two or two of the first three salvoes. --Sfnhltb 05:06, 6 March 2007 (PST)

I think some of what's written at Battleship#Weapons should be copied over. I've never tried it myself, personally; I don't bother engaging battleships until I have an Avenger. What I'd really like is some way to stop Terror Ships before I get Plasma Cannons... two Interceptors armed with Avalanches? Or does it take three?--Ethereal Cereal 21:59, 5 March 2007 (PST)

From the encounter I had yesterday, would suggest 3 is needed, it can trash them so quickly that you need to throw in loads. The one thing I noticed was that Avalanches in some ways seemed better than the Plasma cannons because you can get off a 1-2 rounds of missiles before the Plasma even starts firing due to the range difference, which is critical with your paper thin Interceptors vs the Battleships. --Sfnhltb 04:56, 6 March 2007 (PST)
2 interceptors with avalanches can bring down a terror ship and make it back to base in one piece. I think 10 avalanches will kill it. You do need to do the agressive trick with at least one interceptor to make sure all 6 missiles actually hit.
(Never tried interceptors vs battleship, it sounds suicidal.) --MB 11:56, 6 March 2007 (PST)

Review of Air Combat Mechanics

Moved to its own article Air Combat Mechanics

Operational and Logistic Aspects




  • Seb76 Loader option to relaunch aircraft before they are fully ready.
  • Add link to "Duty Cycle" discussions & table

Patrolling fuel usage

TBD: Summarise fuel consumption for patrol/not, hybrid/not.

I saw somewhere that the skyranger at least uses less fuel when patrolling, but I have this vague recollection that the hybrids don't. Am I right in this or does it need investigating to determine one way or the other? --Sfnhltb 16:05, 5 March 2007 (PST)

You are correct, hybrids don't conserve fuel while patrolling. Only the originals do. --Pi Masta 17:15, 5 March 2007 (PST)
That does appear to be the case. I just tested this with a Firestorm (not an Avenger), and there were a few quirks: fuel consumption was the same whether patrolling or not (which is what you were asking about); fuel readout only decreased in 5% increments (not well-documented); it returned to base when it hit 50% fuel, regardless of distance-to-base (argh). (Skyrangers and Interceptors will stay out below 50%, based on distance.) Fuel consumption was 0.5% of total per minute.
A patrolling Skyranger used up 0.02% of fuel per minute. A constantly-moving one used up 0.0455% per minute. This is more or less consistent with what is documented at Skyranger.--Ethereal Cereal 18:29, 5 March 2007 (PST)

Strategic Aspects

Scoring vs Location of Intercept

I am currently on 23rd January, so should be able to check whether XCOM Activity relates more or less directly to your pay rise at the end of the month fairly soon, but if it does then clearly you will always want to shoot down UFOs over a sponsor country instead of neutral territory (especially the big scoring recovery missions).

--Sfnhltb 06:31, 28 February 2007 (PST)

IIRC the amount of money you get is randomly assigned, though increase, decrease, or no change is based upon 'score', and the country's 'happiness' with XCOM. I think this can be seen by saving near the end of the month and noting the funding changes on each save (w/o doing anything special), I believe each time they will be random amounts (but again the sign of the change is dependent on the score, directly or indirectly).

I'm not sure if a higher score as an effect on the average increase (or conversely lower score with average decrease). It is possible. However I imagine that you are still correct that downing a UFO over a sponsors country is better than over a neutral country. Pi Masta 11:51, 28 February 2007 (PST)

Hmm, we should add a graphic to the wiki showing where the sponsor land masses are.--Ethereal Cereal 12:22, 28 February 2007 (PST)

Yeah I had noticed it was random, I think your starting cash is as well, where the random range comes is was something I will be testing at the end of the current month of the game I am on, which might take a while as I am only playing intermittently (lots of work on atm)

--13:11, 28 February 2007 (PST)

Don't bother with the funding deals. I did this looong ago, both at the StrategyCore forums as well as a complete country-by-country funding breakdown at the forums. Granted, this was for the starting funds, not for subsequent months. But I did run about 2000 trials on that scenario and found that funding was random within a certain range. --Zombie 14:44, 28 February 2007 (PST)

Hmm, well compared to the starting funds that you tested that were almost static overall (unless I am misreading it, +/- 15k or so?), the monthly amount varies a whole lot more, certainly +/- 250k from the average on a given good month I tested briefly to get an idea of it (and could grow more for an even better month I suspect). I would be interested in finding out what exactly affects it, and how responsive it is to key elements you might be able to control (like how beneficial is shooting down more aliens in sponsor country, compared to the same region (if that affects anything at all), and overall.

Btw, in case you still are thinking about the question regarding the discrepancy between your income and expenditure at startup, i can tell you where the 1860000 comes from at least - its in LIGLOB (A0611C00 in backwards hex) - its basically the source of the Finance graph (except score, which comes from XCOM.DAT combined with UIGLOB), which of course assigns it all to Maintenance - which in theory could include 1.7 million for the planes, 300k for the scientists, 250k for the engineers, 160k for the soldiers, and 224k for the maintaince of facilities of the base, so it doesnt solve it, but at least you can eliminate paying for things in trying to work out what it is.

The most obvious answer here is that you pay for craft rental (1.7 mill) and your soldiers (160k) = 1.86 million, and you dont pay for the scientists, engineers or base maintainance. --Sfnhltb 16:41, 28 February 2007 (PST)

The monthly funding (according to the OSG) is determined by these two equations:

Alien activity in country + (Overall alien activity/5)
X-COM activity in country + (Overall X-COM activity/10)

These numbers are compared and if the alien score is greater than X-COM, the country decreases funding by a random amount, but no less than 20%. If X-COM is greater than the alien score, the country increases funding by a random amount, but no greater than 20%. I'm not sure what the upper or lower boundary is. It could be 0%. Who knows, the frequency of the non-20% limits may increase as score does. Suppose the easiest way would be to edit alien score to 0 and X-COM score to something high and check the results. That would correspond to "EXCELLENT" on the End Of Month report. Another test is to edit both X-COM and alien score to zero and check the funding there. This would correspond to "OK" on the EOM report. One thing is for certain, it would take a great many reloads to form any type of conclusion. One of these days I'll have to write up an AHK script and dedicate some computer time to this project. It won't be right away though. --Zombie 21:47, 28 February 2007 (PST)

Ah, that explains something I was seeing - basically if you get double the Alien score, everything is good, if you are less than that everything is bad. When using very large numbers that is, to minimise other factors.
I think the increase is between 5-20%, if they come up as happy. But sometimes even with the same scores they turn out just to be satisified (current game I am playing, overall score 2.6k, alien score was 132 (and I think quite a bit of that I am double counting, country and region)
And yeah, no matter how high the XCOM scores went (very high values in the 4th byte didnt register, but I could get 30k or 60k I think, and there was no change in the range of values to cursory inspection at least. I am fairly sure that happy/satisfied/unhappy is an on/off switch that is fired by a comparision of the scores in a manner as you list above (but there is some randomness in it however).
The scale of the increase in funds seems to be based entirely on the existing funding level, so basically you just get a random percentage value within fixed limits (5-20% on the upswing, havent explored going down enough to say with enough confidence). If US is paying out 10 Million (and you have removed the funding cap, or it wont go higher), values are in the range of 500k to 2 Million if it increases, or 0 if they are only satisfied.
There isnt a whole lot of random numbers it rolls either, which you see with that nice round 10 mill, you get nice neat values spread out every 100k (rounding issues would make it look like there were more possibilities with a smaller existing fund). So its a random int between 5 and 20. Going down is probably a mirror image I would guess, but thats not got any real evidence behind it. --Sfnhltb 18:16, 1 March 2007 (PST)

When do most people bother intercepting?

I'll be frank, I usually don't bother. The Elerium and loot is worth more than the UFO Downed points (funding changes are typically on the order of half a million or less; one Medium Scout and one Large Scout saved from Power Source detonation give $660,000 just in extra Power Sources and Navigations), and I can handle a night mission or two. I only bother intercepting in a few cases:

  • Small Scouts - Downing them doesn't lose anything. Destroying them loses the alien's gun, but they don't generally land and downing them safely is nearly impossible before advanced craft. Pretty easy choice.
  • Alien Retaliation - Nothing on that mission ever lands recoverably, so this is another no-brainer.
  • Terror ships performing Alien Terror - They don't land recoverably. See above.
  • Alien Base flotillas - Unless you've got multiple squads, you can't Ground Assault all four ships in the flotilla. And shooting down some of them breaks up the flotilla (because any that haven't spawned yet will get delayed), so you can get in two Ground Assaults instead of potentially only one. I'll take two Ground Assaults and two Crash Recoveries over a single Ground Assault any day.
  • Alien Infiltration - Not only is there a five-ship flotilla at the end, but Alien Infiltrations have a large and direct impact on X-Com's financing in addition to the points issue. You can't stop them, of course, but you can delay them, and since the mission repeats until all countries in the region are infiltrated, the delays are cumulative (potentially keeping countries in for several months longer than they would otherwise have lasted). So I generally shoot down as many of these as possible.

I just kinda wonder what we should say about this dilemma and where we should say it. Magic9mushroom (talk) 03:57, 7 April 2016 (UTC)

I think this is really best left up to the judgement of the player as the ability to get to a landed UFO can be quite situational. In the early game, unless you are plain lucky or have lots of bases, your Skyranger is most likely not going to be able get to every landed UFO in time. You need the ability to shoot down the UFOs in this instance if only to get some work at the lesser reward. Later in the game you have more options on how to approach the UFOs as you spread out and get better tech to find and deal with them. This is when you can start going for landed UFOs. Much later into the game you'll have enough resources that you end up shooting down the UFOs down simply for the sake of shooting them down and ignoring the crash sites. NKF (talk) 06:11, 7 April 2016 (UTC)

I don't find it difficult at all. You usually detect UFOs on the flight in (or on the flight out, but in that case you can't do anything about them anyway). When you detect it, you send an Interceptor to shadow it and a Skyranger to the area it seems to be heading for, changing it to intercept when it gets close enough. Maximum time for the Skyranger to arrive in any location is 14 hours and it's usually a lot less; you'll generally be detecting the UFOs 4-5 hours before they land and they land for several hours. It's rare that you'll actually be unable to get there until you're dealing with actual antipodes (and at the point you're running Hyper-Wave Decoders on six continents, you're in most cases getting instant detection on UFO appearance, giving you significantly more time). Magic9mushroom (talk) 06:39, 7 April 2016 (UTC)

Oh, something else that factors in that I forgot to mention: interception draws Retaliation, while Ground Assaults don't. Intercepting too early on Superhuman is one of the more plausible ways to lose outright, because if you get a Sectoid Retaliation on your main base in January you'll have a very hard time recovering. Later on, of course, the Retaliation spiral (Retaliation -> shoot down scouts to avoid Base Defence -> more Retaliation) is a good thing for X-Com, but starting it too early is suicide. I know my first attempt at TFTD Superhuman came to an ignominious end that way. Magic9mushroom (talk) 01:22, 7 May 2016 (UTC)

I agree with a lot of points everyone brings up. For me, the decision to intercept instead of going for the landed UFO or ignoring it altogether is situational. Mostly it depends on UFO mission type, craft type, location, severity and quantity.
  • Mission Type: Early in the game you need points to keep your score up in order to eclipse what the aliens can manage themselves and you also need alloys/elerium/bodies/weapons etc for research/manufacturing/funds. If a mission UFO is going to land, I'll wait for it to do so. Why bother wasting a missile on it? (Pending night time missions may prompt an interception to make things safer/easier). Obviously, if there is going to be a Terror Mission, I'd much rather shoot the UFO down so I don't have to deal with the hefty penalty if the mission goes pear shaped, or to defend the stupid civilians. Alien Resupply? C'mon, it always lands so you might as well wait (or ignore). Retaliation? Might as well shoot everything down, you don't want to lose country funding. Research? Ignore for the most part, unless nothing is going on. Harvest? Wait - most land and the ships are easy to recover. Abduction? I normally shoot these down if possible. While not overly critical, I don't want the aliens to get too many points. Alien base building? Yeah, I'll try to, especially with the tougher races. Otherwise the base itself is faster to take out than the UFOs building it.
  • Craft Type: With Small Scouts, it's faster to just shoot them down and destroy them outright rather than waste an X-COM ship with weaker weapons on it. Medium or Large Scouts I'll try to let land. Same for harvesters or abductors. As I mentioned above, wait for the Supply Ships to land and shoot down the Terror Ships. Battleships are the only ship where I have to make a decision on it. Can my troops handle it? Can my ships handle it? Will it land on it's own? What is the race? What is the mission? Those all factor into a final decision.
  • Location: If an alien mission is being carried out halfway around the world, I'm more likely to shoot it down as it takes time for the Skyranger to get there.
  • Severity: As mentioned above, a mission with a higher severity will be met with interceptions.
  • Quantity: If the UFOs arrive one at a time with days between landings, you can go after them while landed as there isn't a rush. What throws a spanner into the works is when the ships arrive in a big wave or group. If all of them are going to land, you can probably get to at least a couple before the rest take off and leave for good so I usually shoot down most of them and leave a couple. Visit the landed ones first, then go after the crashed ones when time permits. --Zombie (talk) 03:52, 9 May 2016 (UTC)

Speed in interception window

Not sure where to put this. But:

When you're reeling a UFO in, it gets closer at 2 range units (1/4 km) per frame.

When you're reeling a UFO out (going back to a more cautious mode), it gets further away at 4 range units (1/2 km) per frame.

When a UFO is escaping, it gets further away at 8 range units (1 km) per frame.

Magic9mushroom (talk) 13:56, 22 August 2020 (UTC)

Old Chat

Ye Olde Bayse Maynetaynanse

Of course the thing that has lead me onto, is trying to work out how it calculates base maintenance. A lift only new base costs 30k (4k for the lift, 26k extra somewhere), and a vanilla starter base costs 224k, but the parts only add up to 169k, so the extra unassigned part raises to 55k. Whats going on?

So I dismantle the starter base (after dumping all loose objects like people, planes and guns), the first Hangar drops the cost by 10k (not 25k), the next one by 4k (huh?), then 10k again for the last hangar, workshop drops it by 35k (correct!), the radar drops it another 35k (way high!), the living quarters are 30k, the lab 35k (a bit high), the stores 35k (massive - 7 times what it should be), and the lift 30k (4k in UFOpedia).

I thought maybe this was messed up somehow because of being the starter base, but it seems to behave the same way in new bases - as I say empty base with lift 30k, lift + stores + small radar = 95k, adding alien containment, stores, living quarters to starter base is 55k up on the starting cost (second stores 10k off when removed, second living quarters 10k, alien containment 35k)

So the same facilities take different maintainance depending on how many you have of them (it seems), and most of them cost different to what it says they do. No idea what the relationship or reasoning is behind all of this.

--Sfnhltb 17:05, 28 February 2007 (PST)

No what's happening is that there are completed 'empty' modules. When you dismantle a facility it doesn't set the days to build to 255 like it should, and instead just puts the dirt tile there. Apparently these completed dirt modules take monthly maintenance (but isn't shown in the monthly costs IIRC). If you want me to find the post I can, but this is something I'm familiar with and in fact the 'editor' I'm making (PyXCom) should be able to fix it. (another thing is even if you build something and dismantle it before it's built, it will still count down and suck your money away)
Atleast I think this is the issue you are having. Pi Masta 19:57, 28 February 2007 (PST)

No I worked it out, I added the basic details to Known_Bugs#Facility_Maintenance_Costs, there might be something additional as you say, as destruction a facility doesnt clear the construction counter as you say - in fact you can see that it keeps construction counters from previous saves as well at times, the clearest indication its doing stuff like this is if you start a game and name your first base something long, say 'ABCDEFG', and then start again and make a new base with a one character 'X', in the BASE.DAT you will see something like 'X CDEFG' (the space indicating actually a null (00) to show end of string). So when you save it doesnt 100% overwrite all bytes, just the minimum it needs to save the information for your current save (which may have errors like you suggest).

--Sfnhltb 20:03, 28 February 2007 (PST)