We are the Mighty
The fleet was first established sometime after the colonization of Reach and the surrounding worlds. It was continuously built up and constructed for the century that followed. By 2552 fleet numbers had risen drastically, with over 100 to 150 warships in-system at any given time.
Following the aftermath of the Battle of Sigma Octanus IV, the Covenant had discovered the location of Reach and proceeded to attack the planet, sparking the Fall of Reach. At the time of the advance force of Covenant ships consisting of a few Covenant corvettes including Ardent Prayer and the CSO-class supercarrier Long Night of Solace.
Although elements of the UNSC Army and Navy were engaged in a pitched battle with Covenant forces throughout the Viery Territory, a large portion of the Epsilon Eridani Fleet, including Captain Jacob Keyes, was being kept ignorant of WINTER CONTINGENCY to facilitate the capture of a Class-Five vessel for use in Operation: RED FLAG.
The Covenant were first detected by Fermion Remote Scanning Outpost, which continued to warn all UNSC forces in-system of the new threat. There were only about 100 ships at Reach at the time, which moved into defensive positions to defend the planet, with 52 more ships on the way. A large nuclear mine field had been set up to detonate the Covenant fleet, which destroyed roughly one hundred enemy ships. The opening salvo of Covenant plasma rounds were mostly blocked by three Refit Stations, letting the fleet fire their first MAC salvo unharmed. When the Covenant fired again however, a crushing 80 UNSC ships were destroyed.
The remaining UNSC ships regrouped with the reinforcements to defend the orbital platforms, but the Covenant began sending hundreds of dropships to the surface of Reach, accompanied by several cruisers to destroy the Orbital Defense Generators. They also used a Covenant supercruiser to sniper the ships of the fleet which were unable to destroy it. It was able to also avoid rounds from the Super MACS. Finally, the UNSC Pillar of Autumn destroyed the supercruiser in an intense battle, but the Autumn was severely damaged and much of the fleet was destroyed. Despite strong defense from UNSC ground forces, the Covenant managed to push through and destroy the generators, letting the remnants of the Covenant fleet move in and glass Reach, destroying the UNSC stragglers.
Only a handful of ships escaped Reach, most of which were badly damaged. The known survivors were the severely damaged Pillar of Autumn which was later destroyed in the Battle of Installation 04, the Charon-class light frigate UNSC Aegis Fate, an ONI Prowler which witnessed the battle and its aftermath, and the UNSC UNSC Gettysburg which was later salvaged to help the survivors of this battle and the Battle of Installation 04 return home. After the Covenant glassed Reach, they moved in on the other in-system colonies, including Tribute. The Battle of Tribute was a short one, with only a fraction of the original fleet there to defend it. The fleet suffered 90% losses and Tribute was presumably glassed.
UNSC Dawn Under Heaven, Halcyon-class
UNSC Pillar of Autumn, Halcyon-class
UNSC Hannibal, Marathon-class
UNSC Leviathan, Marathon-class
UNSC Aegis Fate
UNSC Stalwart Dawn
Remote Sensing Station Fermion
20 Orbital Defense Platforms