Solemn Penance

Regret's Carrier was an Assault Carrier that was used by the Covenant Navy in the First Battle of Earth, and the First Battle of New Mombasa. It was commanded by the High Prophet of Regret, making it distinctive from the other ships of its task force.

First Battle of Earth
The ship arrived in the Sol System on October 19 as a part of a relatively small task force, composed of itself, another Assault Carrier, and thirteen cruisers, expecting to find and uncover the entrance to the Ark. Instead, they ran straight into the heavy defenses of the UNSC Home Fleet, defending humanity's homeworld. While the cruisers engaged the human warships and orbital defense platforms, the carriers used boarding parties of Elites and Grunts to carry antimatter bombs into three platforms, intending to blast a hole large enough for them to circumvent the defenses and reach Earth's surface. Though two were successfully destroyed, the second Assault Carrier was destroyed by the Master Chief, using the bomb from Cairo Station. Regret's ship continued unimpeded, descending to New Mombasa, in Kenya, Africa.

First Battle of Mombasa
Hovering over the city, the ship deployed massive numbers of ground infantry and heavy equipment, including Scarab walkers, intending to drive the UNSC out of the area and begin its excavations. Unfortunately, they had failed to factor Spartan-117 into their plans, and the Covenant forces were forced to try and fend off a UNSC assault, spearheaded by the SPARTAN Supersoldier. Eventually, faced with the possibility of being overrun on the ground, and intercepted by UNSC ships if it tried to escape to orbit, it activated its slipspace drive in-atmosphere, making an emergency jump - dragging a UNSC frigate, In Amber Clad, in its wake. The shockwave from the jump flattened the city, killing everyone, human and Covenant, still remaining. Later, the site was excavated further by the Covenant, uncovering the Portal.

Battle of Installation 05
The Carrier exited slipspace near a second Halo Installation, and the Carrier again deployed its troops, claiming the Ringworld in the name of the Covenant and transmitting numerous messages from the Prophet of Regret himself to the Prophet of Truth, apologizing for his rash actions. As the UNSC forces, again spearheaded by the Master Chief, closed in on the Prophet, managing to assassinate him, the Carrier used its Energy projector to level the temple where the Prophet had been based, planning to kill the Master Chief. Its attempt was unsuccessful.

The ships eventual fate is unknown. While it is possible that it was captured by Rtas 'Vadum and his Special Operations Elites and was the Shadow of Intent, this is never explicitly stated. It may even be unrelated, another Assault Carrier altogether, from the Fleet of Retribution.

Trivia

 * The ship can be seen on the levels Metropolis, Delta Halo and Regret.
 * It is unknown whether the Carrier's exit from slipspace near a second Halo Installation was intentional or accidental.
 * Regret uses a personal warship in Halo: The Cole Protocol, the Infinite Sacrifice. It is unknown whether this was the same ship.