Gray Jacks are decrepit Hybrids that have almost outgrown their bodies. They are not an individual strain of Chimera, since they are simply elderly Hybrids.
In Resistance: Fall of Man, the Gray Jack's description implies that Hybrids grow as they age, their limbs gradually elongating. This increased size places tremendous strain on their cooling units over time, which are not designed to cool them at this size, and their high metabolic rate begins to cook the creatures from the inside-out. Gray Jacks are the final stage of this process and are near-death, resulting in a necrotic appearance and a characteristic odor of decaying flesh.
These Chimera are unarmed and appear to be frail, however, they possess a long reach and wicked claws, giving them a deadly attack. Intel states that those wounded by a strike from a Gray Jack suffer injuries that are very diffic
ult to clean and highly prone to infection, resulting in a high mortality rate. Gray Jacks are never seen on the front line of combat, implying the Chimera do not regard them favorably as military units.
After the events of Resistance: Fall of Man, Gray Jacks are reported to be seen very rarely among Chimeran forces. It is believed that they are "dying" out, and have already begun to vanish from Europe as well asMenials and other older forms of Chimera. It is not clear why Hybrids no longer grow as they age in later games.