The game is set in 1999. In that year, close-air support had been a thing for some decades already. The game could be programmed to let XCOM operatives call in air strikes like so:
In the Geoscape view, the interceptor (or other armed craft) needs to be patrolling near the ground assault site / terror site, like close enough so the site is within it's radar circle, before the ground assault mission starts.
At least one soldier in the skyranger needs to be equipped with a new item: the Forward Air Controller Radio, which can be bought on the market and is similar in size to a medikit. (Alternatively, the air strike could be called using a coloured smoke bomb, but this seems more like WWII tech than 1999).
During the mission in the battlescape, the soldier with the radio can hold it in hand and "use" it like a medikit or mind probe. It will have an "ammo" count equivalent to whatever weapons are loaded on the nearby interceptor.
The soldier can use the FAC radio on any square in the map to call in an air strike from patrolling interceptor on that place.
The interceptor does not have to graphically appear in the battlescape view, just it's munitions. It can be modeled as a dummy invisible object above the view from which the munitions come. It may be simplest to have the munitions originate above the center of the battlescape map for targets near the sides, and from the nearest side for targets near the center of the map, so the rounds come in at an angle like from an aircraft.
Each use of the FAC radio will cause the interceptor to launch at the target area one of its rockets or a burst of its cannon, depending on what it is loaded with, until it runs out of ammo. The weapon effects should be thus:
- Cannon strafing run - an auto fire burst of 20 AP cannon rounds that sprays the designated area. The sprites for the cannon bullets can be the same as those for the HWP cannon shells. Since the cannon can shoot down UFOs, it should be damaging enough to have a random chance to make a hole in the skin of a landed UFO, like make 1 - 2 holes in a UFO for each strafing run. The area of the spread should be quite big as the cannon is not that accurate, like it should cover one field in size, so it might also riddle a farmhouse with bullet holes.
- Stingray rocket - Can use the sprite from the HWP rocket. One Stingray rocket should do HE damage enough to make a 1 square hole in a UFO skin. It should also blow up most of a farmhouse. It should be more accurate than the cannon but also not be too precise, maybe hit within a 3 x 3 square area of the aim point.
- Avalanche rocket - One Avalanche rocket shoud do HE damage enough to make a bigger hole in a UFO, like 2-3 square big, and completely destroy a farmhouse. Accuracy should be better than for the stingray.
There can also be air strikes using lasers, plasma or fusion ball aircraft weapons when those are available.
These air strikes also run the risk of friendly fire as they are not 100% accurate and have an area effect so players will have to use them with caution. On Terror sites they may cause civilian collateral damage.
After the misssion ends, back in the geoscape view the interceptor will have to RTB to rearm.
An alternative to having a radio object carried by a soldier as the means to trigger an air strike is to use the Minimap in the player's interface and have the player click on the minimap to call in the air strike there. After all, the landed skyranger should have a radio that can call in the air strike. This will also add an element of map reading skill to the use of the air strike mechanic. Just add some buttons to the minimap to call in the airstrike.
