Some Units have a “Stealth” ability, which allows them to be invisible to other Empires, and move in and out of their Territories unnoticed.
The Stealth ability is supported by the following Unit attributes:
An Army is only as stealthy as its least stealthy Unit – in other words, the maximum possible Stealth at the Army level is equal to the lowest Stealth capacity of its Units.
If an Army is composed of several Stealth Units, and one of them has lower Stealth than the others, then the entire Army will act with the same Stealth as that Unit.
Units with no Stealth ability are assumed to have a Stealth capacity of 0, so mixing Stealth and non-Stealth Units in the same Army will cause the Stealth Units to become visible.
While an Army is Concealed, it is invisible to all other Empires, except the Allies with whom you have signed an Intelligence Coalition Treaty.
In addition to being invisible, Concealed Armies have the following capabilities:
However, any aggressive action undertaken while Concealed will instantly reveal the Army.
Ambushes are a special type of Battle that occurs when an Army moves onto a tile that appears empty, but in fact is occupied by a Concealed Army.
During an Ambush, special rules apply depending on the role of each Army:
Finally, if the ambushing Army wins the battle, it will instantly refill its Stealth gauge and remain Concealed. If it Retreats or is defeated, its Stealth gauge will drop to 0.
Empires desiring to protect themselves against covert actions need to beef up their Territories’ Detection capabilities. As soon as the first Stealth Units become available during the Medieval Era, different Constructibles and Units begin providing Detection as well.
Detection sources always operate on a “best value only” mode; If you have several Armies in a Territory, only the Army with the highest Detection will be counted. The same rule applies to Districts and Squadrons within a Territory.
As a result, a Territory’s Detection is the sum of up to three sources:
Additionally, some Empire-wide Detection bonuses can be obtained when you complete the Satellite Network National Project.
Concealed Armies in a Territory lose as much Stealth per turn as the best Detection of the Territory they are in (see Hostile Detection below), until their Stealth gauge reaches 0 and they are revealed. Whenever a Stealth Army enters one of your Territories with Detection higher than 0, you will get a Notification alerting you of covert forces within your borders.
The Intelligence view, accessible from the bottom left of the screen, will enable you to compare the different Detection capabilities on the Territories you can see. You can use this view to find promising targets for undercover activities, or to evaluate your own weak spots.
Since Armies and patrolling Squadrons also provide Detection, it is possible that Empires other than the Territory’s owner have the best Detection over that Territory.
If this happens, your own Stealth units will not be able to regenerate Stealth, even within your own borders, unless they are standing on Districts that offer protection from external Detection : Garrisons, Administrative Centers, and City Centers.