The Eight Day War

The Eight Day War, formerly known as Operation: Black Knight, was a UNSC attempt to retrieve 20 HAVOK Nuclear Devices from a Republic Of Joseph Outpost, 90 kilometers from Los Carlos in a remote forest. This was one of the deadliest UNSC engagements in it's time period with rebels, due to famine, rouge UNSC Military units, and the captured UNSC Deaf Leopard, which killed thousands of marines and destroyed the UNSC Deathly Hallow. Despite the rebel victory, the UNSC secured a small victory, whom destroyed a large weapon cache and numerous vehicles, enough to disband the RoJ chapter near Los Carlos.
== Background ==
For 14 years before The Eight Day War, Cygnus II and Roost had been ruled by two factions; The UNSC and The Republic Of Joseph, which had the upper-hand after capturing multiple frigates, destroyers, vehicles, and over 500 FERNIS and HAVOK nuclear devices in their arsenal. To make things worse for the UNSC, both planets had a small defense, which were both easily defeated by the RoJ's 300,000 members. After the Human-Covenant War began, the RoJ began drafting random civilians between the ages of 18 through 50, forcibly training them, brainwashing them, and sending them to battle, which by early 2526, had over 700,000 members. 
The Republic Of Joseph's only weakness was the religion they followed, which eventually lead to a bloody civil war against one another, and in the end, made themselves vulnerable to the SPARTANS. Another factor that made them weak was that another rebel group was rising, the Freedom Rebel Party, which was the remnants of infamous groups such as the Klu Klux Klan, the Nazi's, Survivalists, and The Black Panthers.
== The Battle ==
On February 4th, 2526, at 0400 hours, 20,000 Marines, 500 ODST's, and the UNSC Champion Of The Haters arrived on Cygnus II in order to retrieve 20 HAVOK nuclear devices, the UNSC Diamond Back, and crush the rebellion. At 1500 hours on that same day, the marines found and destroyed thirteen rebel bases, with light casualties. On February 7th, the fleet passed through San Jefferson, and destroyed most of the city on orders from ONI. By February 10th, the UNSC destroyed over 70 rebel bases and retrieved 3 HAVOK nukes, but only killed about 600 rebels. 
On February 12th, the marines arrived at the "base of operations" for the RoJ on Cygnus II. Before the marines could fire on the base, however, the captured UNSC Deaf Leopard rammed itself into the UNSC Deathly Hollow, which in turn crashed into the Champion. The Destroyer was then destroyed by a HAVOK via remote detonator, before a RoJ EMP was detonated over the battlefield, before the rebels attacked with Scorpions, Shortswords, and Warthogs from shielded garages. Within 20 minutes, the once proud UNSC Fleet was left in tatters, with over 13,000 marines dead. The remaining marines fled, but most were gunned down by Wolf Spider Turrets and landmines. By the early hours of the 13th, only about 481 marines survived by the time of being evacuated, and more died due to famine.
== Aftermath ==
Both the UNSC and ONI, whom feared of the moral decline by the result of the battle, kept the Operation a closely guarded secret, and was instead replaced by the destruction of San Jefferson. A few days after the Eight Day War, a SPARTAN Team went missing in the area, and wasn't seen again until May, with a reporter, who tried to spread the truth to the public, but was dismissed as a rumor. By March of 2553, the battle, after 26 years, finally went public, along with Operation: MOUNTAIN FURY and Operation: BRONCOS