There's no where really safe from these guys.James Stevenson
The Hydra Tank was an enemy created by the Agorians and encountered in the Krell Canyon. Later in the game, gray Elite Hydra Tanks are encountered that have more health and different, stronger attacks. They are found in the Agorian Arena. It was a big red machine with three serpent-like heads that were capable of releasing fire. After a certain amount its health was depleted, the robot created a forcefield preventing Ratchet from inflicting further damage, but also exposed a set of vulnerable Versa-fuses at the base of each serpentine head. At this time, Ratchet could use the OmniWrench Millennium 12's kinetic tether to pull off the Versa-fuses connecting one of the heads to the forcefield generator. When all three heads were removed, the creature exploded.
To defeat the Hydra Tank, use a rapid-fire weapon such as the Constructo Pistol, Buzz Blades, or if you have acquired it, the RYNO V. Switch between two of these weapons while evading the attacks of the tank. In Krell Canyon, it is especially useful to stand on higher ground, such as boulders or small plateaus, usually near an ammo crate spawn. By doing so, Ratchet will remain clear of harm when the tank emits an array of oscillating lasers across the ground's surface, ensuring the easy destruction of the tank.
Behind the scenes
These are named after the Greek hydra from ancient mythology. Their heads resemble those of the legendary monster, and like it, the Hydra Tank has multiple heads.
There was an enemy cut from the first game also called the hydra.
The Hydra Tank appears as an easter egg in Resistance 3, at the end of the game Jack Capelli is seen playing with a toy Hydra Tank.