To attempt a UFO Interception select the global intercept command or click on the base you want the ship to be launched from. The second option only lists the ships at that base, where the general list is good for launching dropships but may be a little too cluttered for launching interceptors once you have a number of them.
While selecting the interceptor's destination, world time is halted. You can continue to scroll the map by way of the controls or the more recommended centre-on-location command (RMB). This is a great way to pause the map in order to survey the globe if there are too many things happening at the same time - and if your Geoscape time is moving too fast for your liking.
- Elerium-based ships have the highest acceleration and maximum speed but the shortest air time. Conventional aircraft have the longest air time, but are very slow. By virtue of its speed and large fuel capacity, the Avenger has the longest range overall, about twice that of a Skyranger.
- Your ship autopilot prefers to move along lines of latitude (parallel to the equator) for long-range travel. This is especially noticeable when charting trans-polar routes: the ship will circle around the pole instead of flying straight across it. You can shorten the route taken by directing the ship to several intermediate waypoints along a straight line towards your destination. This way, you can probably squeeze a little more range out of the Lightning, which has very little air-time.
- Note that when you tell your craft to intercept a UFO, they will head directly for it. This is fine when you have plenty of fuel to spare or if it is headed directly towards you. If the UFO is traveling at an oblique angle to your base however, you will find that your craft will follow a roughly parabolic arc in its pursuit, using up more fuel and time than is strictly necessary. It may be worth trying to judge an approximate interception point and sending your craft to that waypoint and then re-targetting as the distance closes.
- With slower conventional aircraft (or faster UFOs), you may end up in a protracted, frustrating tail chase, waiting for the UFO to slow down and/or double back on itself. Even when it does, the poor intercept algorithms (and/or poor acceleration?) of conventional craft mean you will often miss the UFO on the turn.
- While chasing a UFO, it may land. It will stop and turn to a green icon. At that point, if you feel tactically strong enough, launch an immediate UFO Ground Assault mission against the landed UFO. Keep the interceptor stationed above the UFO, in case it moves off. UFO Ground Assaults are harder than Crash Recovery missions, for the simple reason that more aliens are left alive to fight back. However, the rewards are correspondingly greater. An interceptor can do you a better service by tracking a UFO to a landing site, than it can by forcing the UFO to crash, and much less by destroying the UFO (which earns only victory points, no material gains).
- There is a 'scramble' delay while your aircraft gets airborne, and before it starts moving toward the target. For Interceptors this delay is about 4 minutes after issuing the order to Intercept.
- Ship weapons will fire continuously at set intervals (based on weapon type,weapon speed, current attack mode, and possibly range) at an enemy target as long as it's within maximum firing range (represented by the range bars) - until it runs out of ammo. After one weapon type runs out of ammo, the ship will move to the maximum range of the remaining weapon (if any).
- Multiple ships (up to 4), can join the battle by way of minimising the controls while in stand-off and waiting for extra friendlies to arrive on the scene. This can be key if you only have regular Interceptors when a Terror Ship or Battleship turns up.
- The three different attack modes have various effects. Attack mode affects the distance of the interceptor and the UFO, and the closer you are, the faster the combat between UFO and interceptor can become. This means the interceptor and UFO can be exposed to more fire from each other's weapons, possibly at a shorter range, and are possibly engaged by additional (shorter range) weapons. Another effect is that the more aggressive the attack mode, the harder it is for either side to break off, and escape. Note, the selected attack mode for each interceptor controls the exchange of fire between that individual interceptor and the UFO only. Apparently, if you have two ships engaging the UFO at the same time using different attack modes, one on a more cautious mode will give and receive fire at a slower rate than a ship that's on a more Aggressive mode.
- When chasing a ship, if the UFO starts to back off and you minimise the window, you must wait until your interceptor starts to catch up with the UFO before you re-open the intercept window otherwise the interception will break off and will only start again once the UFO is back in stand-off range. If you let the UFO get away, the interception will halt and will only resume when the ship catches up with the UFO again - the net result is the same. The only difference is that the first method keeps the intercept window open while the other mode exits and then enters the intercept screen. There's no real advantage to this, except perhaps in TFTD when your ships are near the coast.
- When intercepting a UFO, you may want to take care where you actually complete the interception - sometimes you might have little choice, but if you shoot down a UFO over water you will not be able to perform a UFO Crash Recovery mission later. In addition shooting down a UFO (and later performing a mission on the crash site) over a sponsor countries airspace will cause increase in XCOM activity for that month (based on the score awarded), which helps keep that country happy and might persuade them to increase their funding at the end of the month.
- Also be aware when intercepting using Cautious attack that there is a bug when you fire you final shots that will cause them to always miss. Try to change modes before the last shot.
- Multiple ships take a UFO down faster, and the UFO splits its fire between all of them that are in range in turn, randomly, making each of your craft more likely to survive longer on average. Try to make it so that all your ships come into firing range at the same time so you can maximise the advantage of bringing them all together.
The Interception Window shows several things. It graphically displays the range, type, and remaining ammunition of the Interceptor's weapons with small brackets, shows shots traveling to each combatant, indicates distance to and relative size of the UFO, and shows the amount of damage that the interception craft has taken so far.
There are several commands available to you in Interception.
- Standoff (Top Left): Aircraft maintains standoff range with UFO (70km). Neither side can shoot due to range. If selected during active combat, the aircraft ceases fire immediately (regardless of whether any weapons are in range) and attempts to open the range out to stand-off range, and hold there.
- Cautious Attack (Top Right): Interceptor will close to the UFO until it can fire its weapon with the longest range (unless the aircraft carries identical paired weapons, only one weapon will fire.) Should this weapon's ammo be depleted, the Interceptor will then close until the other weapon can be brought to bear. Should the Interceptor be damaged by alien fire, it will retreat back to Standoff range and mode. The UFO has a good chance of successfully fleeing if the interceptor's top speed is lower.
- Standard Attack (Top-middle Left): The interceptor will close with UFO until it can fire both weapons and then maintain that distance. (If paired weapons are carried, this is the same as Cautious) If the interceptor is damaged badly in a single shot, it will retreat back to Standoff range and mode. The UFO has a chance of successfully fleeing if the interceptor's top speed is lower.
- Aggressive Attack (Top-middle Right): Interceptor will attempt to get as close as possible to the UFO, firing both weapons as soon and as often as possible. Interception craft will not retreat regardless of damage, unless switched to a different combat mode. UFO will have difficulty fleeing combat even if interceptor is slower.
- Disengage (Bottom-middle Right): Interception craft will immediately cease firing (regardless of whether any weapons are in range), and attempt to open the range beyond Interception range, > 75km. Once out of the Interception window, on the Geoscape the aircraft will disengage the UFO and start returning to base, though it can be ordered to do something else as soon as combat is broken.
- View UFO (Bottom Right): View a side picture of the UFO; the same picture that will appear in the UFOpaedia upon successfully gaining the details of the vessel from an alien Engineer. Can be used to identify targets.
- Minimise Window (Outside Top Left). Returns to the Geoscape view. Used to wait until target is over land, or until the aircraft closes to Intercept range, or to allow other aircraft to join the battle. Can only be activated when at Stand-off range.
Every time the weapon from an interceptor hits, it will deal anywhere from 50% to 100% of the damage rating listed on Craft Armaments. If a UFO has taken 50% or more of its damage capacity in Interception damage, it will crash-land (assuming it is over land) and X-COM will be credited UFO Grounding points and can later launch a UFO Crash Recovery raid to clean up anything left. If the UFO takes 100% or more of its damage capacity without crash landing, the UFO will be destroyed. No crash site will be generated, and X-COM is credited with UFO Destroyed points (which are double the points given for Grounding the UFO. It should be noted that some UFOs yield enough points in recoverable loot to make it preferable to ground them instead of destroy them). More to the point, UFO Crash Recovery missions yield tactical experience, saleable loot, and researchable items, all of which are essential to winning the game and usually (but not always) more important than scoring points.
You can use this command to make ships act as mobile radars, sending them out to areas of suspected alien activity, or just as radar pickets to cover areas distant from your base (similar to an aircraft carrier's Sentry early warning aircraft). Particularly when looking for Alien Bases you will need to patrol a suspect area, but your crafts localised but powerful onboard radars can be useful elsewhere, and means they can be sent after a UFO which has left your tracking radius and should be able to reacquire them if you can anticipate the UFOs movement in the interim. Another potential benefit is that Interceptors and Skyrangers will consume half as much fuel when patrolling than when flying around at top speed. This means they can stay "on station" for twice as long. This can make one or two conventional aircraft useful to have around even in the later game when they are otherwise mostly redundant in their original roles.