Operation: THRAWN

"Why Thrawn? Well, apparently Freemount's a big fan of some 20th Century sci-fi series."

- Annabel Morrigan and Carolyn Webster discuss the operation.

Operation: THRAWN was the UNSC Navy's plan for the naval defence of the Epsilon Eridani System as part of the larger Winter Contingency in the event of a Covenant attack on the system. Though it was executed during the Covenant's invasion of the system in 2552, Admiral Roland Freemount rescinded the order when he realised the true size of the invading Covenant force, and redirected the forces involved to Earth.

History
After the fall of the Outer Colonies in 2536, the UNSC became aware that however effective the Cole Protocol was proving to be, it would only be a matter of time before the Covenant came within striking distance of major colonies such as Earth or Reach. As a result, a number of worst-case scenario tactical plans were developed for the defence of these systems, Operation: THRAWN among them. It was drafted by Admiral Roland Freemount, the commander of the Epsilon Eridani Defence Fleet.

In Scots, the word "thrawn" means a combination of obstinacy, assertiveness, and more than a hint of willful perversity. The name was chosen by Freemount, and the UNSC Fleet Command considered this naming to apt, given Humanity's struggle against the Covenant and, reckoning that the name revealed nothing classified about the operation, approved it. However, it is also believed that Freemount chose the name due to his familiarity with the Expanded Universe of the 20th Century science fiction film series Star Wars, as the tactics of the operation are strikingly similar to those employed by the character Grand Admiral Thrawn.

The operation
The operation envisioned two task forces stationed in the Jericho (Hip 15689, not to be confused with the Lambda Serpentis System) and Tantalus (Luyten 726-8) Systems, the two closest systems to Epsilon Eridani. Task Force Jericho consisted of seventy-five capital ships, while Task Force Tantalus was composed of eighty-six capital ships. The one-hundred-and-fifty-two-ship strong Epsilon Eridani Defence Fleet, together with twenty Orbital Defence Platforms remained in the Reach system as the first line of defence. Upon the arrival of a Covenant fleet in the system, warned by Remote Sensing Outposts, the commander at Reach would send a message via Slipbeacon to the two task forces, ordering them to reinforce him. The fleet at Reach would hold its own making use of the ODPs and nuclear mines to thin out the Covenant force until the two task forces arrived, with Task Force Jericho coming out from Reach's superior Safe Slipspace Entry Point (SSEP), and Task Force Tantalus re-entering normal space at Reach's inferior SSEP. The two forces would then either, depending on the situation, blockade the SSEPs, preventing the Covenant force from escaping quickly and forcing them to make a sublight retreat out of the system's gravity well, during which ships could be picked off one by one, or spread out and encircle the Covenant force in order to destroy them in a "Cauldron Battle". After the Battle of Sigma Octanus IV, the plan was adapted to include the defence of the fleet by sacrificial refit stations.

Assumptions
The planners of the operation made a number of assumptions for the operation. The first, and in hindsight, possibly the most glaring, was the belief that the Covenant would not commit more than two hundred ships to an attack on Reach. In fairness, the UNSC had never seen the Covenant commit more than several dozen ships to any offensive (the Battle of Psi Serpentis being an exception, since that was a defensive Covenant operation), and believed that the Covenant did not have the military or political ability to commit more than a hundred ships to any operation. This assumption was proved fatally wrong during the Battle of Reach, where the overwhelming Covenant numbers encouraged Freemount to divert the Jericho and Tantalus forces to Earth rather than lose badly-needed ships. The planners also assumed that Covenant Slipspace engines were party to the same restrictions as the UNSC's - that they could only enter or exit Slipspace at SSEPs, or outside the system's gravity well, whereas in reality, Covenant Slipspace engines allow a Covenant ship to exit Slipspace inside a planet's atmosphere, much less a system's gravity well. However, this interpretation was completely consistent with tactics displayed by the Covenant so far in the war; coming out of Slipspace far from the system to ascertain the defences, followed by a sublight approach in-system and a fast withdrawal through the SSEPs after destroying the enemy. Covenant tactics at the Battle of Reach were entirely consistent with this interpretation, the only difference being their massive, unheard-of numbers.

Fire plans
Two fire plans for the UNSC forces were devised for the battle, Avalanche and Waterfall.

Fire Plan Avalanche
Avalanche called for the UNSC forces to open fire all at once in a single massive salvo in order to destroy the largest number of Covenant ships at a time. Nuclear mines deployed by Prowlers would further be used to thin out the Covenant numbers and give the UNSC ships time to recharge their MAC guns while being covered by the ODPs. The plan envisioned heavy losses for the Covenant and was devised as a "numbers equaliser" in the event of the UNSC being outnumbered. It was the plan adopted for use in the Battle of Reach.

Fire Plan Waterfall
Waterfall envisioned groups of three to five UNSC ships opening fire in a rippled fashion at the Covenant fleet, ensuring a continuous "stream" of fire directed at the Covenant. Three to five ships would direct their fire against a single Covenant ship in order to collapse its shields with the first two MAC rounds and deliver a killing blow with the third and a salvo of Archer Missiles. The next group of ships would then take over and give the previous group time to recharge its MACs. Waterfall called for nuclear mines to be detonated among the Covenant fleet before opening fire, in contrast to Avalanche, in order to collapse Covenant shields before the MAC rounds hit and increase their effectiveness. It was envisioned that Waterfall would be used after Task Forces Jericho and Tantalus arrived.

In practice
THRAWN was activated as part of the UNSC's larger Winter Contingency during the Battle of Reach in August 2552. The UNSC's assessment of the Covenant's ability to project a large number of ships into UNSC space was proven fatally wrong by the battle: Freemount ordered the Tantalus and Jericho task forces into the system upon first hearing of the Covenant attack, but as the Covenant's massive numbers became more clear, he ordered the two task forces to divert to Earth in order to reinforce its defences, believing that the Covenant force would be able to weather its losses and break through their defences no matter what varient of the operation they tried, and that with the fall of Reach, there would be no further stop-points before Sol for the Covenant. These task forces arrived the day the Battle of Earth started in October 2552.

Despite being outnumbered, the UNSC force was able to inflict disproportionate losses upon the Covenant through Fire Plan Avalanche. Many more kills, possibly to the extent of being decisive, may have been scored had it not been for the presence of the Covenant Supercruiser, which destroyed dozens of ships with its energy projector before it was subdued by the UNSC Pillar of Autumn.