Infiltration

A unit that is infiltrated is invisible and cannot be targeted by normal means.

Certain units can fight while infiltrated, while others cannot.

These open up new possibilities
Some maps have entire routes that are fully in cover, for example Blood River. Thus, certain units can cross the map while fully infiltrated.

Some maps have routes that have cover en route. These can be used as ambush points.

Certain maps are flooded with negative cover, which reduces movement speed and increases the damage received by units within it. Infiltrator units have a notable advantage here.

Infiltrated units can be revealed by units with Keen Sight
Keen Sight refers to the ability of a unit to reveal infiltrators.

Units marked by an icon in their production facility (such as a Barracks), possess Keen Sight.

This includes the commander of every race, in addition to other units.

Turrets no longer detect infiltrators. LP3s now have Keen Sight, instead.

Notably, the Chaos Bloodthirster now has Keen Sight.

Infiltrators can also be revealed by anything that can ground attack
This includes such weapons as grenade launchers, whirlwinds, and even frag grenades.

It also includes psyker powers such as smite.

Minefields also have Keen Sight.

Dark Eldar's piercing vision also provides Keen Sight.

Revealed infiltrated units cannot quickly re-infiltrate
Damaging a unit with a weapon disables the target unit's infiltration for 5 seconds. This means that:
 * To re-infiltrate you need to disengage from combat.


 * To prevent enemy infiltrate you can chase them.


 * Infiltrator units with escape mechanics (such as Stealth Suit Jump) have an advantage over Infiltrator units without (such as Chaos Space Marines).


 * Well placed turrets, while they cannot themselves reveal a unit, they can ensure a unit cannot re-infiltrate in your base.

Keen Sight adds a dimension of tactics to the game
The distance at which units reveal infiltrators is much lower than the distance that they can see.

Those with keens sight often must gap close to expose infiltrators.

Infiltrated units that come at a flank often forces the commander to go out of position to deal with the threat.

A commander that is chasing around an infiltrated unit cannot disrupt the gunline or easily participate in duels.

A commander on low HP is less able to deal with infiltrators, putting your flank or backline at risk.

A player who loses the commander duels may want to invest in other sources of Keen Sight, to shore up this weakness. For example, skull probes.

Keen Sight encourages infiltrator units to attack enemy positions away from the enemy commander(s).

In summary, infiltrators encourages:
 * Positional tactics
 * Map awareness
 * Multi-tasking of units across the map

Exhaustive list of Keen Sight units
For context, 25 is the range of a Tactical Space Marine Bolter.