UFO Incursions (Apocalypse)

Alien Craft Type and Quantity Appearing in Mega-Primus

In General

Aliens send their craft through a 'portal', called a Dimension Gate, appearing at random locations and random positions within the cityscape as time progresses. It is an invunerable device.
UFOs are 'grown' in the Alien Dimension at the start of the week and only of types dependant on the number of weeks elasped in the game.
Note: the following is behind the curtain' information and is never known to a player.

The Schedule

Each Monday, the Aliens randomly set a time and day to perform missions for this new week. When a mission is due according to Monday's timetable, the aliens will choose from a list (relevant for game-weeks elasped) a mission parameter. Once decided on the type of mission to perform, the aliens will allocate the UFOs present in the Alien Dimension to immediately spawn into Mega-Primus.
An alien craft will appear from the portals in sequence according to the specific mission chosen, but will randomly choose which one after each craft has appeared. Also, they may use just one, or all three. (...and may be exploited by a save/load after each appearance)

The Roles

The UFOs listed as "Escort" craft are designated to escort and protect the primary ships. They will make all haste to primary ship and protect it from being attacked. If the primary ship they are escorting is shot down, they will move to another primary ship to protect that instead. If all primary ships are shot down, the escorts will realize they have nothing to protect and make their way to a dimension gate to leave. ... conversely, primary ships do not care whether their escorts are still around, and will attempt to fulfil their mission even if all escorts are destroyed.

Primary ships will give up on their mission if they receive too much damage, and will attempt to retreat.

Some UFOs on the Infiltration and Overspawn Drop tables are listed as "Bombing" craft. These craft will bomb a building, as though on an Bombing mission.

Destroying the Control Chamber building permanently halts the production of alien craft. It also triggers a special incursion not found on these tables - the next time an alien mission is scheduled, all remaining UFOs (except Probes) will swarm out of the Dimension Gates and start tearing down Mega-Primus as though on a very large Bombing mission. This final battle is typically referred to as "the Apocalypse mission".

UFO Production

Week
1	9	9
2	2	4	3	2
3	2	4	2	2		3
4	1	2	1	1	2	2
5		1		1	1	1	2
6		1		1	1		1	1
7		1			1		1	1	1
8		1				1	1	1		1
9								1	1
10		1					1
11				1		1			1	1
12							1	1
13		1		1					1
14								1		1
15									1
16+							1	1	1	1
Maximum	15	15	6	6	6	6	6	6	4	2

Mission Chance

Week	Infiltration	Base Assault	Bombing	Overspawn Drop
1-3	100%	0%	0%	0%
4	90%	0%	10%	0%
5-6	80%	10%	10%	0%
7	70%	10%	10%	10%*
8	50%	20%	10%	20%
9-11	40%	20%	20%	20%
12	30%	30%	20%	20%
13	30%	20%	30%	20%
14	40%	20%	20%	20%
15-18	30%	20%	20%	30%
19	20%	20%	30%	30%
20+	10%	40%	20%	30%

*An Overspawn drop in Week 7 can't actually happen, as there are guaranteed to be no Motherships available (none have spawned yet).

Infiltration Fleets

These are the standard type of UFO incursion for the majority of the early game, which peters out as the weeks go on in favor of more direct aggression. Infiltration fleets consist of one to three primary craft, usually with escorts to protect them (as seen on the table below). When they appear in Mega-Primus, the primary craft will fly directly to a pre-selected target destination, hover over it for several seconds and attempt to deploy a squad of aliens to infiltrate the building via a transport beam (i.e. 'the grey tube'). Destroying the craft before it reaches its destination will prevent this. If the tube has already appeared, it is possible to prevent the UFO from succeessfully completing its transport by destroying it before the beam has finished. UFOs which successfully deposit their troops will then immediately move to the dimension gates to return to the Alien Dimension, leaving players to have to send squads to investigate those buildings for aliens. If left unchecked, the target organization's infiltration percentage will go up after several hours and the aliens may continue to spread to nearby buildings and organizations, creating an even bigger problem for X-Com over time. When a primary UFO craft for this mission type escapes via the dimension gates, that craft's assigned escort(s) will then immediately attempt to escape as well (this rule holds true for most if not all incursions).

If the Aliens choose to target an X-com base for infiltration, this will trigger a base defence mission instead.

Mission	Primary	Escort	Bombing	Week
1				1
2				1
3				2
4				2
5				2
6				4
7				3
8*				4
9				3
10				3
11				4
12				4
13				5
14				8
15				8
16*				7
17**				7
18				7
19				8
20				8

*These fleets will never appear, as the ships required will also fulfil a higher-priority fleet.

**This fleet can appear as long as the aliens have at least one Battleship and one Escort Ship (though two Battleships will still appear in Mega-Primus). This is the result of a bug in the spawn routine; instead of checking whether there are two Battleships, it checks whether there is one Battleship twice.

• UFO fleets led by Transporters or Assault Ships are always on Infiltration missions.

Bombing Fleets

Likely the second or type of fleet the player will have to contend with (or third depending on luck), 'Bombing' fleets are exactly that - UFOs sent to cause as much destruction to the city, craft and X-Com as possible. These typically consist of primary craft using disruptor bombs or multi-warhead missiles while escorted by Fast Attack or stronger escort ships using medium or larger disruptor beams. On the plus side, players will not have to worry about tactical missions other than to seize any downed UFOs, as they will not be attempting to deposit troops in buildings. These fleets will remain in the city much longer than infiltration fleets before pulling back to the alien dimension, and can cause massive damage if left unchecked. While they can be a great source of captured UFOs and technology, a bombing fleet should never be underestimated, as it can pose one of the greatest threats to unprepared X-Com craft and personnel. If an X-Com base tile containing the 'person' icon is destroyed, that base's personnel may be killed as a result.

Mission	Primary	Escort	Week
1			4
2			4
3			5
4			4
5			5
6			6
7			7
8			9
9			9
10			8

• Bombing fleets appear from Week 4 onwards.

Base Assault Fleets

This fleet type is the reason players want to build Security Stations and keep armed personnel to secure X-Com facilities. Base Assault Fleets will spend their time in the city scanning buildings with a sparkling blue scanning beam resembling blue 'rain' with the express purpose of seeking out X-Com facilities. Once located, the aliens will send at least one UFO in all future missions of this type loaded with troops with one singular purpose: Invading and destroying the discovered base. This can be prevented by shooting down any incoming UFOs before they can locate your base, or the troop transport if they've already found it (though it can be an impossible shell game to determine just which primary UFO is the one bringing the invaders). There is an urban legend that this beam can cause an organisation to be immediately infiltrated, leading to the infamous misnomer 'micronoid rain' for the beam.

Mission	Primary	Escort	Week
1			5
2			5
3			5
4			5
5			5
6			5
7			5
8			5
9			7
10			8

• Base Assault fleets can appear from Week 5 onwards.

Overspawn Drop Fleets

Exactly what it sounds: An Alien Mothership (usually with escort craft) is sent to drop an Overspawn to attack the city directly. This type of mission can *only* occur if the aliens currently have a mothership available to deploy.

Mission	Primary	Escort	Bombing	Week
1				8
2				8
3				8
4				8
5				11

• Overspawn drops can appear from Week 8 onwards.
• A fleet with two Motherships is guaranteed to be on an Overspawn Drop mission.

See Also

• Alien Ships
• Cityscape Fighting
• Alien Ship Combat