Battle of the 78th Thema

The Battle of the 78th Thema was an engagement fought between the Forerunners and the Flood in Path Terrulian within the 78th Thema. One of the penultimate battles of the Forerunner-Flood war, it ended in a rare Forerunner victory in this stage of the conflict. The battle itself represented a portion of a larger engagement, waged across four themas.

Background
With the remaining Forerunners escorted to safety, eventually to be evacuated to the greater Ark, the Forerunners concentrated their last battle fleets to the defense of a region of space consisting of four themas standing in the brink of complete infestation. Fleets were withdrawn from Path Kural, which had been lost to the Flood, becoming part of a Burn.

The organization and force distribution of the battle followed the established doctrine of Forerunner space warfare, fundamentally based upon abstract membranes extending into higher dimensions and combining Slipstream space transit vectors along with scalars measuring potential outcomes. These multi-dimensional membranes or "branes" made up a hypersphere which combined slipspace transit arrays and tactical probability scalars, both of which were adjusted as the engagement progressed and outcomes were determined.

The action in the 78th Thema was part of the Warrior-Servant forces' first clench, under the command of the Falchion. The clench encompassed nineteen systems, all of which had been formerly linked by star roads. The first flex of the membrane leading to the clench began at the inner edges of Path Terrulian, a pre-stellar nebular region surrounded by old, cooling stars, as well as an abundance of asteroids as well as rocky and icy planets. The Falchion's forces in the clench consisted of twelve Fortress-class vessels, largely stationary due to reconciliation debt, acting as apex control stations for 700,000 smaller Harrier-class vessels. The opposing Flood force was estimated to comprise over 100,000 vessels, the most powerful of which being 400 dreadnoughts.

Battle
The Flood fleet arrived at Path Terrulian en masse, using Precursor neural physics superluminal transit. Seemingly caught by surprise by the Forerunner military presence in the region, the Flood ships were momentarily vulnerable upon arrival as they radiated multiversal residues. The Falchion immediately ordered a group of cloaked harriers, positioned in advance, to launch a series of precision strikes against the incoming Flood ships. Instead of using easily detectable directed energy weapons or projectiles, they utilized their gravity slings to launch local asteroids at high velocities into the emergence fields of the Flood-controlled vessels, enabling the harriers to remain untraceable for a time. The barrage of asteroids interfered with the transmission of the arriving ships, vaporizing a half of the vessels directly, while the rest managed to evade and reposition themselves, scattering across several thousand kilometers. A multi-pronged force of uncloaked harriers engaged the remaining Flood vessels with their energy beams, quickly destroying one-third of the infected ships.

The remaining Flood ships were rapidly rendered harmless; mostly intact but lacking any offensive capability. The Falchion intended to salvage the Flood ships' corrupted ancillas, deploying ancillas under his own command to examine the ships and retrieve their designators, which were then delivered to sentinels deployed from one of the apex fortresses. Aided by the harriers, the sentinels breached the shields and hulls of the drifting Flood vessels and boarded them in order to reprogram their control ancillas. At first, this effort seemed to be successful, as the Forerunner automatons had supposedly been proofed against the Flood's logic plague. However, upon entry and contact with the infected ships' ancillas, the sentinels were rapidly subverted by the Flood. As a result, the Forerunners were forced to destroy the infested vessels one by one, along with the corrupted sentinels.

Aftermath
The isolated tactical victory in the battle did little to slow the Flood's spread across the galaxy; the Capital's system was conquered by the Flood shortly afterward, resulting in the governance and strategic command of the ecumene being transferred to the greater Ark. Acknowledging the futility of the attempts to salvage Flood-controlled ships and ancillas due to the constantly adapting nature of the logic plague, the Forerunners soon completely abandoned this program in favor of destroying any infested ships outright.

List of appearances

 * Halo: Silentium