Coordinated Stage

The Coordinated Stage is the second stage of a Flood infestation. During this stage, Flood population begins to rapidly increase, and, once sufficient biomass has been found, Pure Forms begin to be sent into combat. After this the next stage of Flood infection may begin. On the verge of initiating the Coordinated Stage, the Proto-Gravemind continues to be built until it reaches the status of Compound Mind or Gravemind. It is at this point that the Flood becomes significantly more organized (communicating via thoughts and attack strategically) and subsequently more lethal.

Occurrence
This stage has occurred several times;
 * The first was the Gravemind’s conception from the planet of G617g, the original Flood which eventually gave way to the Gravemind who made war with the Forerunners and was believed to be destroyed during the first firing of the Halo Array. * The second occurred on the Infinite Succor, an agricultural support ship which was part of the Covenant’s Fleet of Particular Justice. The on-board Legate, a San ‘Shyuum who bore responsibility for the vessel, eventually became part of the biomass reserves being built on the ship by Combat Forms – it is believed to have been in the process of transforming into a Proto-Gravemind before a Covenant operative sent the vessel careening at the speed of light toward the system’s sun.
 * Not far away, on a ship just above Installation 04, Captain Jacob Keyes had become an anchor for what appeared to be a Proto-Gravemind. This entity, however, had been taken care of as the Master Chief obtained the Captain's neural implants.
 * At some point, a catastrophic containment failure on Installation 05 released the Flood into a quarantine zone, which, eventually facilitated the creation of a Proto-Gravemind. This became the last known Gravemind, the one which existed during the Halo trilogy.

Trivia
This is the stage that most resembles the Flood in Halo 2