The ISA fleet designated Battle Group Mandrake is a military task force that participated in Operation Archangel during the Second Extrasolar War. Placed under the command of Colonel Jan Templar, Battle Group Mandrake, along with other battle groups, was part of the second wave of the assault force that invaded Helghan. It consisted of 24 ISA Cruisers transporting the Battle Group's ground forces and Intruder dropships, with its flagship being the New Sun.
Battle Group Mandrake was successful in capturing Pyrrhus City as well as destroying the Arc Tower defenses of the capital, making it the more successful of the two other Battle Groups sent to Helghan. Despite early success, the Battle Group suffered very heavy casualties, with most of its cruisers destroyed by Helghast forces and the majority of its ground troops annihilated by the nuclear weapon Red Dust. Finally, the Battle Group's ultimate objective of capturing the dictator Scolar Visari has failed after he was killed by Special Forces Sergeant Rico Velasquez.
The surviving marines and naval evacuees of Battle Group Mandrake were then stranded at Visari Palace as a massive Helghast fleet began its counterattack on the Battle Group's few remaining ISA Cruisers. Given orders to evacuate the planet, the ISA's ordered withdrawal soon became a rout, with many units isolated and destroyed piecemeal by the overwhelming and enraged Helghast forces. Further worsening matters, the remaining ISA Cruisers, that were unable to reach orbit, were finally destroyed by the Helghast's MAWLRs and fleet counterattack, leaving the stranded ISA ground troops little choice but to regroup and fight on for mere survival.
Six months later, after overcoming numerous hardships and setbacks, the small ISA remnant finally found a way to escape Helghan after fighting tooth and nail across the planet. Eventually, the ISA forces board a Helghast space station and hijack several Helghast strike fighters. They then use the fighters to destroy the experimental cruiser of Helghast corporate chairman Jorhan Stahl, who planned to bombard Earth with hundreds of irradiated petrusite warheads, thus killing or irradiating millions of people on the UCN capital world and causing the UCN to capitulate. The experimental cruiser's destructive payload was then detonated over Helghan due to secondary explosions, violently irradiating the entire planet and obliterating the entirety of a massive Helghast invasion fleet destined for Earth. Managing to avoid the cataclysmic explosion in time, the remaining ISA troops of Battle Group Mandrake onboard the hijacked strike fighters then made their way back home to Vekta.
Out of the +180,000 men and women in Battle Group Mandrake that were sent to Helghan, only a dozen of the stranded marines, and a single known cruiser made it back to Vekta alive. What cruisers of the ISA Navy that survived served as escorts to the Helghast refugees following the Terracide.
- The Battle Group was named after the late General Mandrake, whom Templar met during the events of Killzone: Liberation.
- Battle Group Mandrake was just one of the 12 ISA Battle Groups that took part in the Helghan invasion, however, not much is known about the rest of the Battle Groups. Whether they succeeded in their missions and survived the Helghast counterattack or not is unknown.