Battle of Kamchatka

In 2558 a battle took place at Kamchatka, fought between the forces of the United Nations Space Command, Jul 'Mdama's Covenant, and the Prometheans on the icy planet of Kamchatka. During the battle Dr. Catherine Halsey was rescued by UNSC forces and Jul 'Mdama was assassinated.

Background
Before the Great Purification, Kamchatka was an astroengineered Forerunner world, created to serve as a link to the galaxy-spanning network the Domain.

In 2558, a long-dead communications hub on the planet's surface activated, attracting the attention of Jul 'Mdama's Covenant. Jul 'Mdama's Covenant moved to control the planet while Dr. Halsey, under temporary alliance with Covenant leader Jul 'Mdama, studied the relay and discovered that her old AI Cortana was alive. All the while, Jul 'Mdama's Covenant would gather and use the Caspar system as a staging area.

Approximately three weeks before the battle, Dr. Halsey contacted the UNSC, warning of an incoming event caused by Cortana. However, the UNSC didn't act upon that information immediately.

UNSC plans
Analysts at the Office of Naval Intelligence deemed that a strike on these forces at Caspar could potentially do substantial damage against the Covenant faction, and give the UNSC an edge. By October 17, 2558, plans were put in place to attack Jul's forces in the system as part of Operation: ANCHORITE, and to retrieve Dr. Halsey as part of Operation: DESINENCE. While ANCHORITE was known widely across the UNSC Infinity with it being part of a briefing letter, DESINENCE was not, with little information being discussed about it. Part of the overall attack plans included a second wave of forces deployed from the Infinity. The Infinity would also bring a complement of s.

Betrayal
At some point prior to Osiris' arrival onto the planet, Promethean forces turned against Jul 'Mdama's.

DESINENCE
"Fireteam Osiris, the light is green."

- Jameson Locke to Osiris, prior to jumping into battle.

The deployed Fireteam Osiris, a Spartan-IV special operations squad, to retrieve Halsey and assassinate Jul 'Mdama if possible. They dropped from low orbit by Pelican and landed amidst an enormous ship and ground battle, as Cortana had taken control of Jul's Prometheans and was unleashing them against him. Jul 'Mdama's Covenant made little headway, with the constructs managing to bring down a blockade runner and force back a Kraken walker. The chaos from the Prometheans' rebellion provided Osiris cover from 'Mdama's Covenant, allowing them to sneak to the temple where 'Mdama and Halsey were stationed.

After reaching the temple, Osiris attacked Jul's Zealot guards while Spartan Jameson Locke faced off against Supreme Leader in melee combat. After a short fight, Locke was able to kill Jul with his combat knife, bringing an end to his tyranny. Fireteam Osiris then took custody of Dr. Halsey and she was brought back to the Infinity to aid in the search for the Guardians.

Aftermath
"Kelly-087"

- Fred-104

With Jul 'Mdama dead and the Prometheans now against them, his Covenant troops became desperate. Some of them fled to the Argent Moon to retrieve their soldiers scavenging the station, though most of them were killed in the attempt after Blue Team scuttled the station to keep it out of enemy hands, destroying several Covenant warships in the process. Most of the rest regrouped on Sanghelios, attempting an attack on the Vadam clan burial grounds in hopes of a revenge attack against the Arbiter. Covenant forces at that were under the joint control of several other high-ranking members of the faction including Kitun 'Arach.

Trivia

 * Halo Waypoint's Canon Fodder article Fifty Caliber states that "unconfirmed reports" about the Battle of Kamchatka claim there might have been a temporary alliance between Fireteam Osiris and the Sangheili Kitun 'Arach of Jul's forces. This is a reference to the Enemy of my Enemy achievement, in which the player(s) can choose to save a Sangheili Warrior assaulting a hill against Promethean Soldiers, turning him from an enemy to an ally.
 * The bodies and wreckages of Swords of Sanghelios soldiers and Banshees are scattered throughout the level Osiris. While it is possible they participated in the battle, their use as game assets suggests they might be stand-ins for the deceased forces of Jul 'Mdama's Covenant.

List of appearances

 * Halo 5: Guardians
 * Halo: Legacy of Onyx
 * Halo: Bad Blood
 * Halo: Official Spartan Field Manual