Timeline

2519
John becomes the squad leader.
 * 12/7/2519

2525
The ninth age of reclamation begins for the covenant.
 * ?/?/2525

Contact with Harvest, an outer colony is lost shortly after the colony itself had made contact with an unknown object. The Colonial Military Administration sends the scout ship Argo to investigate.
 * 3/2/2525

The Argo arrives in-system and makes one confirmation transmission. No further reports are received.
 * 20/4/2525

The Spartans undergo a radical series of biological, neurological, and physiological alterations. 30 die, 12 are permanently disabled, 33 successfully adapt the alterations.
 * 9/3/2525

The Spartans first "official" mission, to infiltrate the rebel base on Eridanus and capture the rebel leader, Colonel Robert Watts, is successful.
 * 12/9/2525

A UNSC battle group consisting of one Destroyer (Heracles, Captain Veredi) and two Frigates (Arabia and Vostok) enter the Harvest system and discover that everything on the planet has been completely incinerated, and the surface melted down to glass. In orbit around the remains of the colony, is a single alien ship, which proceeded to attack the battle group, destroying both Arabia and Vostok and badly damaging the Heracles. Intercepted communications identify the enemy as The Covenant. The message "Your destruction is the will of the Gods... and we are their instrument" is broadcast in UNSC language.
 * 7/10/2525

Vice Admiral Preston Cole mobilizes the largest fleet in human history to retake Harvest.
 * 1/11/2525

The Spartans learn of the attack of the Covenant at Harvest and Project MJOLNIR commences. CPO Mendez leaves to train next group of Spartans.
 * 2/11/2525

Project MJOLNIR, a comprehensive package of scientifically enhanced armour, custom-tailored to the biologically augmented Spartans, and is introduced to John and his squad at the UNSC Damascus Materials Testing Facility, on the planet Chi Ceti-4. The Spartans (now decked out in Mjolnir armour) destroy a Covenant ship by carrying a nuke onboard, inside the energy shield.
 * 27/11/2525

2531
Cole's war fleet engages the alien warship responsible for the decimation of the colony, scoring a victory (though the battle cost Cole two-thirds of his battle group). Only a last minute tactical inspiration turned the tide of battle. After returning to Earth, Cole-promoted to Admiral-learns that a number of outlying colonies have been destroyed, leaving behind no survivors. Cole begins to move his fleet around, trying to intercept the invaders. Ground and ship-to-ship battles begin in earnest, raging throughout the Outer Colonies. During one ground engagement, Human forces capture one of the aliens. Before succumbing to his wounds, interrogators learn that the aliens refer to themselves as "the Covenant" (roughly translated).

2535
In the course of four short years, Cole's forces are hammered, despite his excellent leadership and tactical brilliance. It is simply a matter of being outgunned; Covenant kill ratios tend to top four to one in ship-to-ship combat. By 2535, virtually all of the Outer Colony worlds have been destroyed by the Covenant. The "Cole Protocol" is established by military order: all human vessels must ensure that Covenant forces do not find Earth. Human ships must-when forced to withdraw-not move on to an Earth bound vector, even if that means jumping without proper navigational calculations. If blind jumps are not possible, the ship's captain must order self-destruction if capture is imminent. In addition, it is also imperative that the powerful ship A.I. data cores not fall into Covenant hands, so part of this protocol involves either the removal or destruction of the ship's A.I. in extreme situations.

Jericho VII in the Lambda Serpentis system falls. Master Chief, on board the UNSC Destroyer Resolute under Captain de Blanc, is allowed to view as the Covenant fleet glasses the planet.
 * 12/2/2535

2536
Covenant forces begin to swarm into the Inner Colonies. For several years the war falls into a pattern: humans win isolated battles, typically during ground operations, but at a horrible cost. In space combat, the humans are losing at a precipitous rate, and one by one, the colonies fall.

2550
The Pillar of Autumn is refit to serve near Zeta Doradus.

2552
John rejoins the remaining Spartans (except for three that are otherwise engaged) in the FLEETCOM Military Complex on Reach, where they learn of their next mission: To acquire a Covenant vessel, navigate to the Covenant home world, and return with captured Covenant leadership.
 * 27/8/2552

A Covenant fleet is discovered by Ensign William Lovell on UNSC Remote Scanning Outpost Archimedes, entering the Sigma Octanus system. Commander Keyes, on board the UNSC Destroyer Iroquois, takes on 4 medium-tonnage Covenant craft (two frigates, one destroyer, one carrier), and destroys 3 of them in what becomes known as the 'Keyes Loop'. The Carrier heads to Sigma Octanus IV and drops Covenant troops, invading the city of Cote D'Azur. Keyes is promoted to Captain by Admiral Stanforth.
 * 17/7/2552

The Spartans and the Marines engage Covenant forces on the ground, eventually nuking Cote D'Azur and most of the Covenant invasion force (but very few Humans), while 4 dozen UNSC ships engage 20 Covenant craft. Seven human craft survive. The Iroquois destroys a stealth ship receiving an encrypted transmission from the surface. Once this ship is destroyed, the surviving Covenant ships break off and flee. The Iroquois heads back to Reach for debriefing. A Covenant tracker attaches itself, unseen, to the Iroquois' hull.
 * 18/7/2552

The Master Chief is debriefed by ONI at Camp Hathcock, Reach, on the events of Cote D'Azur.
 * 12/8/2552

The Pillar of Autumn is chosen by Dr. Halsey and Cortana (with Keyes as Captain) to handle a secret mission that Dr. Halsey is planning.
 * 25/8/2552

The Master Chief gets a neural interface upgrade and new armour with built-in Covenant shield technology. He is also introduced to Cortana, an A.I. created from Dr. Halsey's own neural patterns.
 * 29/8/2552

Cortana gets revenge on Colonel Ackerson, part of ONI's Special Warfare branch, for attempting to eliminate Cortana and Master Chief - she gets him transferred to the front. Bypassing several other colonies, the Covenant arrive at Reach and begin what has become all too familiar to the embattled Human forces: the destruction of the planet.The Spartans are divided into two teams: Red and Blue. John and the rest of Blue team (Linda and James), while on an orbital mission to ensure that a NAV database stays out of Covenant hands, end up onboard the Pillar of Autumn when she jumps away from the Reach system to evade Covenant forces. James is lost and Linda is mortally wounded, and the subsequent mission on Halo is left to the Master Chief to complete. The Covenant take the surface of Reach, and Red team splits, one group to retrieve Admiral Whitcomb, while the rest hole up in ONI's Castle Base underground facility with Dr. Halsey. The Spartans receive parts of a MJOLNIR Mark V upgrade and new weapons, while Dr. Halsey learns of Colonel Ackerson's mysterious plans, plans that seem to involve "her" Spartans.
 * 30/8/2552

Lieutenant Wagner returns to Earth and reports on the evident destruction of Reach to Colonel Ackerson, Admiral Hood, and General Strauss at an ONI facility in Sydney, Australia.
 * 4/9/2552

The Time/Date Record Anomaly of Sep 23, 2552 most likely rejoins the timeline here. Dr. Halsey and members of Red team discover an enigmatic shard in an ancient installation below the ONI facility. Blue team joins with team Gamma to retrieve Admiral Whitcomb, and rejoin the rest of Red team who have been besieged by the Covenant, who apparently revere the artefact that the humans have found.
 * 7/9/2552

The remaining Spartans, Admiral Whitcomb, Dr. Halsey, Sgt. Johnson, Lieutenant Haverson, Warrant Officer Polaski, and Corporal Locklear jump to Slipspace on board the Covenant/Human hybrid ship Gettysburg-Ascendant Justice, and discover that the shard seems to have the ability to bend both space and time.
 * ??/??/2552

The Gettysburg/Ascendant Justice arrives for refit and provisioning in Eridanus system and meets with the rebels under Governor Jiles. Dr. Halsey sedates Spartan 087, Kelly, and absconds with her on Governor Jiles ship, a Chiroptera-class vessel, the smallest UNSC classification that contains an SFTE. Before she goes, she gives the alien artefact to Corporal Locklear, with implicit instructions to destroy it.
 * 12/9/2552

Admiral Whitcomb and Lieutenant Haverson destroy the majority of the surrounding Covenant fleet by detonating the Unyielding Hierophant. John, Linda, Will, and Fred, the last known remaining Spartans, along with Sgt. Johnson, and, of course, Cortana, depart for Earth to warn of the impending Covenant invasion.
 * 13/9/2552

The Pillar Of Autumn arrives at Halo. The covenant attack and force the pillar of autumn’s crew to evacuate to the newly discovered ring world. Captain keyes is captured by the covenant, he is brought to the ccs class battle cruiser: the truth and reconciliation.Chief rescues a large number of marines, taking them onboard the pelican: echo 419.
 * 19/9/2552

Chief and a number of marines make their way into the truth and reconciliation. Chief, Keyes and some prisoners, escape the covenant on a drop-ship.A pair of Pelican’s transport troops, containing Master Chief, to the Island where the ‘silent cartographer’ a map room that can show the location of the Control Room is. After saving the new information into Cortana’s data-banks, the two take Echo-419 through a path of underground tunnels the the area where the Control room is.Chief finds a group of Marines that were not ‘wiped-out’ like the rest of the other Marine groups in the area. They lend him their Scorpion main battle tank. Chief brings the platoon, along with another Chief enters the Control room, he is warned that weapons cash that Keyes is looking for is actually a Forerunner base, and that Halo isn’t covenant. He runs to Echo-419 for a lift.Chief land in a swampy area. Whilst exploring around, he discovers the ‘Flood’.Chief finally escapes from the labyrinth of the under-ground research facility via lift, he finds a team of soldiers scared half to death, waiting for Echo-419. Chief takes control of the Platoon, when Echo-419 is almost at a tower that they chose to meet at, is almost there, Chief is captured by the ‘Monitor’ of installation 04, who uses the Halo network to teleport each other to the ‘Library’.
 * 20/9/2552

Chief goes on a search to find the ‘Index’ a Key that can activate Halo’s firing sequence.Chief reaches the top-floor of the Library, after killing at least 200 ‘Flood’. As soon as he grabs hold of the key, 343 guilty spark teleports themselves to the Control room.When Halo is mealy seconds away from firing, cortana, still inside the computer system’s, cancels the firing order. 343 guilty spark sends out a message of war to the sentinels. Chief destroys the 3 pulse generators that create the energy used to activate halo. Chief is then teleported with Cortana to a Covenant cruiser, where Keyes is being held.The Chief is to late, Keyes has been taken over by the ‘Flood’. Chief takes the neural interface, out of Keyes by literally punching his brains out. The duo capture a Banshee, and lock on course for the Pillar of Autumn. The Master Chief and Cortana, onboard a Longsword in the debris field of the destroyed Halo, find oneRemaining Pelican containing Sgt. Johnson, Lieutenant Haverson, Warrant Officer Polaski, Corporal Locklear, and a set of cryotubes containing Spartan 058, Linda.
 * 21/9/2552
 * 22/9/2552

The Master Chief, Cortana, Linda, Polaski, Sgt. Johnson, Haverson, and Locklear depart for ReachVia Slipspace aboard the Covenant Flagship Ascendant Justice, captured near the Halo debris field.A Time/Date Record Anomaly continues from this point in the narrative, resolved above on Sep 7, 2552.
 * 23/9/2552

The High-Prophet of Regret prepares his private fleet for an endless search for the other Rings, without authorization from the other two high-prophets The survivors of the Pillar of Autumn land on UNSCDF ODA142 "Cairo”.
 * 19/10/2552

Mjolnir MK VI arrives at Cairo from Songnim Corporation, and Chief is the first one to ‘test’ it.The council deems the High-Covenant Commander a Heretic, he is sentenced to death.Whilst the Commander is attending his punishment ceremony, on the Cairo, Chief and others, are awarded a medal for their actions on the Pillar of Autumn.The High-Prophet of Regret’s fleet discovers Earth, thinking it is just another Colony; they attack without messaging the other High-Prophet.Chief successfully destroys the Second Carrier, but the first Covenant ship is already deploying its soldiers.Chief lands in new Mombassa, Africa. He drives out many Covenant patrols out of the City. But the Carrier containing the Prophet of regret makes a jump, inside the city. In amber clad reaches inside the carrier’s shields, gets sucked into the vortex, along with half of the City.The commander is made the Arbiter by the noble prophets of Truth and Mercy. He goes on his first mission, to find and kill the heretic leader. After killing him, ‘Tartarus’ captures 343 guilty spark.
 * 20/10/2552

Regrets Carrier and In Amber Clad reach Halo 05.Chief kills Regret in a forerunner sea palace. He just gets out of the building when the fleet destroys it, whilst unconscious; he is dragged down under water by a mysterious tentacle creature. The Arbiter is sent on a secret mission to retrieve the ‘index’. The Brutes throw him down in to the depths of the ring-world. They mark Civil War!
 * 21/10/2552

The Creature reveals itself as the Flood intelligence of this ring.He sends both chief and the arbiter on a secret mission.Chief is teleported to the covenant holy city, high charity. He runs after the Prophets.The Arbiter is teleported near the control room; he gets his revenge on the Brutes.The Drones and jackals join forces with the brutes and Prophets, now it is the Grunts, Elites and hunters against the Brutes, Jackals, Drones and Prophets.Chief is too late; truth has left with the index. Chief is told by mercy, before he dies of a flood infection, that truth is going to use a forerunner ship to destroy all life on earth.Chief fights his way through wave after wave of flood, looking for the forerunner ships energy-transfer unit. Chief gets caught in the transfer field, and is thrown into the ship seconds away from launching.The Arbiter fails to pull the Index from the control panel; he was forced to fight tarterus first. Halo is Activated, but Miranda pulls out the Index, a remote activation is then needed from the ‘Ark’.Chief, onboard the forerunner ship, transmits a message to the Cairo why he’s aboard that ship; ‘Sir, Finishing this Fight…’
 * 22/10/2552