Tyranids - Infestation: The arrival of the Hive Ship and its fleet of escorts initiates the next stage of a Tyranid planetary invasion. As a powerful synaptic node of the Hive Mind, the Hive Ship disrupts the local Warp in a radius of several light years, unleashing the disruption of FTL travel and astrotelepathic communications that is known as the "Shadow in the Warp." By the time one of these massive voidfaring biomechanical constructs has arrived, it is often too late for a planet to send out an astropathic or other psychic cry for help.Even vessels sent to defend a system under threat of Tyranid attack may be unable to exit the Immaterium in a system that has come under the influence of the Shadow in the Warp. Once the Hive Ship has come into range of a target planet, it immediately begins to launch a rain of Mycetic Spores into the atmosphere and towards the planet's surface.Some of these pods are filled with microbial life. These hostile alien micro-organisms immediately begin to change the planet's atmosphere, oceans, soil, flora, and fauna. Complex organic molecules are broken down and recreated in formats that are best suited for absorption by the swarm. Other spores bear more complex Tyranid bioforms.Some of these, including the various strains of Gaunts and Gargoyles, immediately begin preparing for the assaults that are to come. Other strains begin to burrow deeper into the planet's crust. These may include Mawlocs and Trygons. As these creatures burrow, they plant the spores that can later grow into Capillary Towers and Spore Chimneys. Other organisms may use the tunnels these massive bioforms create to access a planet's mineral wealth and subterranean life in the shelter of the tunnels.At the same time that this rain of devastation begins, those Genestealers and Lictors which have already infested the planet reveal themselves. Using the knowledge that they have obtained and the hybrid fauna they have spawned, these creatures sow confusion through the ranks of the defenders. By selectively targeting officers and communications hubs, the infiltrators of a Genestealer Cult can effectively delay or even compromise a planet's defences.During this phase of the encroachment, a planet's defenders must take rapid and decisive action or all hope may be lost. Cutting the attack off at its source is the optimal solution. If the Hive Ship can be destroyed, the remainder of the Tyranid fleet may lose its psychic cohesion, falling into confusion and even cannibalism. This presents the defenders with an opportunity to divide and conquer the remaining Tyranid forces.While less effective, destroying Mycetic Spores as they fall to the planet may also help the cause. Even the massive bulk of a Hive Ship has a limit to its resources. Each spore destroyed may mean greatly fewer Tyranid war organisms to face on the ground.The Tyranid Hive Mind possesses the ability to make a tactical assessment and modify its strategy. On admittedly rare occasions, a fleet facing unexpectedly stiff resistance may break off the assault and retreat to attack an alternative target that will require the expenditure of fewer resources.Countermeasures against Genestealers and their hybrid xenophile ilk are crucial to this stage. With astrotelepathy likely restricted, any additional loss of communications on the planet could quickly doom the defenders. Extensive security measures must be taken to preserve the integrity of all communication and command centres.