Waves are the primary attack mode of the AI. A wave consists of a group of ships sent from another galaxy through a wormhole by a Warp Gate.
Waves are periodically sent by each AI with a frequency and size that depend on several factors such as the AI's Difficulty, the current AI Progress and the AI Type. Composition depends on what the controlling AI is able to use.
Waves target only eligible planets. To be eligible, a planet must have a warp gate or be adjacent to a planet with a warp gate. Regular waves target only Human planets and spawn at a wormhole leading to a planet with a warp gate. Thus, destroying warp gates on planets adjacent to Human planets deny the AIs the ability to send waves through at least one wormhole (several if that planet is next to several Human planets). That strategy is called gate raid by the community. The name displayed over a wormhole leading to an AI planet with no warp gate on it has an orange tint instead of the usual reddish color. On the galaxy map, the "Hostile Wormhole" display lists the number of wave-eligible wormholes leading to that planet.
Destroying all warp gates adjacent to a Human planet completely deny waves on that planet. That can save turrets and defense on it but at the cost of a raised AIP due to warp gate removal. Also, if all warp gates leading to Human territory are destroyed (or if all Human Orbital Command Stations adjacent to warp gates are destroyed), the AI will send waves on their own planets and the warped fleets will immediately join the Threat.
Several AI units have the Warp Gate ability. There are three different kinds of Warp Gate abilities: Wave Only, Reinforce Only (which is used by the Reinforcement mechanism) and Full, which combines the two. Only Wave and Full are able to launch waves, and not only the Warp Gate itself has it, but also the Alarm Post, the AI Eyes and the mobile Warp Gate Guardian. Players planning a gate raid must be on the lookout for these kind of units as destroying the warp gate would be useless.
Waves are announced at least some minutes before landing: an orange line with a countdown is displayed on the upper left corner of the screen with ship quantity, controlling AI and the targeted planet if the wave is detected.
Waves can be detected with any unit with the Warp Detection ability. All Human Orbital Command Stations has that ability. Several mobile military units also have it, such as the Zenith Starship, the MkV Missile Frigate and the Sentinel Frigate. If a wave targets a planet on which Human players have a warp detector unit, the name of that planet will be displayed alongside the timer and ship quantity. Else, "???" will be displayed.
The Advanced Warp Detection ability counts as a Warp Detection ability but also color with an orange tint the specific wormhole by which the wave will emerge. Few units have this ability, such as the economical command station, the Sentinel Frigate and, or course, the Advanced Warp Sensor.
If the Warp Relay plot is enabled, the AI may build a warp relay which acts as a warp gate but also allow waves to reach further. (See the plot's page for more details.)
The Cross Planet Waves on/off option in the game's lobby somewhat change the behavior of regular waves. Instead of directly emerging from the wormhole, the warped fleet spawns at the warp gate itself and immediately join the Threat fleet, attacking only on the best occasion. While these waves target AI planets, Human players can rarely detect them.
The Raid Engine is an AI structures that launches waves on adjacent planets (even if AI controlled) if Human forces are present on them. This is the rare case where having a mobile warp sensor unit is useful. The various response the AI may employ to threaten any Hacking attempt also contains waves that can target non-Human-controlled planets.
The Warp Counterattack Guard Post, enable by the Plot of the same name, is able to launch a wave upon destruction that can target any Human planet, regardless of warp gate adjacency. In this special case where a wave lands with no adjacent warp gate, the warped fleet spawns somewhere at the edge of the gravity well of the targeted planet. Warp detection works as usual for this special kind of waves.