Halcyon-class cruiser

"A dozen Covenant superior battleships against a single Halcyon-class cruiser. Given those odds, I'm content with three...make that four kills."

- Cortana, during the Battle of Installation 04.

The Halcyon-class cruiser (hull classification symbol: C) was a distinguished class of light cruisers which saw service in the Insurrection and later the Human-Covenant War. Originally shot down by the UNSC on the grounds for its lack of tactical viability, the Halcyon would be mocked for being the slowest, most underarmed and underpowered cruiser developed of the twenty-sixth century. Notable only for its unusually-strong honeycomb superstructure, the Halcyon 's advantages would prove too limiting and it would be quickly replaced by its successor, the.

The Halcyon would embark on a limited production run, with only fifty ever being built. Although some would be hastily retrofitted with more weapons and hangars in an attempt to increase their combat viability, by 2521 the entire class was reassigned into reserve fleets. They would be saved from certain scrapping with the arrival of the Covenant, with their complicated superstructure actually allowing them to survive far longer than their replacements against their quarry's exotic weaponry. As a result, they were pulled out of the dockyards and refitted up to modern standards, and proved to be one of the most powerful ships at the UNSC's disposal. However, even these updated cruisers would take horrendous losses, ensuring that each Halcyon was deployed sparingly. Nevertheless, the class would become an icon symbolizing durability, and would inspire the UNSC to adopt the similarly-shaped.

Armour and superstructure
Widely regarded as their sole meaning for existence, these cruisers became renowned for their durability. A sophisticated system of supporting skeletons, a mix of internal and external plating, and emergency repair systems work together to expertly hold the ship together while under fire, and this configuration continued to remain unique even decades after the Halcyon 's launch. Each component alone is capable of mitigating damage with greater efficiency than any other competitor on the market, but are combined to increase the tolerance so much that they exceeded the structural guidelines the Navy placed upon contemporary battleships and heavy carriers.

Originally unique to this model of cruiser, the first eleven ships were host to a powerful series of interconnected supports, organized into octagonal shapes throughout the hull. Developed by Dr. Robert McLees himself, this 'honeycomb' structure uses a combination of hyperdense diamond-tungsten composite beams, propriety heavy-duty hydraulics, and internal armor rolled over the most vulnerable rooms on the vessel, such as the bridge, ammunition storerooms, and engineering sections. The framework was never compromised in favor of streamlining the process of fitting the ship's interior spaces, which is why that structural pillars can be seen passing through walkways in places. Outside of the supports organized around the central hangar, the octagons around the core were reinforced with four cross beams in their center to handle the increased stress. When supported by appropriate shock-absorbing and temperature mitigation equipment, this resulted in an incredibly rigid and resilient spaceframe. For example, Halcyon-class cruisers equipped with this could suffer the loss of 90% of their armor and damage to all compartments and still remain able to participate in combat. In an extreme example, the UNSC Pillar of Autumn was able to participate in two high-energy space battles and a subsequent crash through a Halo's atmosphere, while remaining more-or-less intact. However, such ridiculous reinforcement was costly in terms of resources required and mass, and took up a huge amount of internal volume that could go to better offensive systems, powerplants, and more consumables. In addition, the way the beams were ran through the hull meant that their fabrication and replacement was a longer affair. For these reasons, all Flight I starships that followed the first three ships saw various changes to their frames; the last of these craft, the UNSC Roman Blue, included three Class-7 Service Corridors and shrunk the portion of the hull using the honeycomb supports by 15%.

The succeeding 37 ships would use a different framing scheme altogether, which was based on an improved reinforcement scheme found in Marathon-class heavy cruisers. This replaced the honeycomb scheme with a cluster of hexagonal cores, which drastically changed into a conventional skeleton found on all later Reyes-McLees' capital ships. Cheaper industrial sapphire was used in the cross beams, and the spinal struts were enlarged to cope with the extra stress they found themselves with. Although a sound idea that reduced their tonnage from 9 to 8.3 million metric tonnes, the new shock absorbers used to divert away kinetic energy proved vulnerable to high-temperatures, and relied on an intact power distribution system to function properly. Because of this, while on paper the Flight II Halcyon-class cruisers had strength tolerances that exceeded that put on early heavy cruisers, in practice they suffered from weaker resilience when compared to their successors. As a result, many of these ships had to either undertake extensive refits to bring them back up to the standards of the first group, or scrapped to free up parts for their peers.

Armament
Even at the time of their launch, Halcyon-class cruisers were already considered under-performing in offensive capabilities. Their primary armament consisted of a single the 13M6R1 Magnetic Accelerator Cannon, a light coil spinal weapon that ran about 600 meters through the upper half of the cruiser. This specific model is configured to launch somewhat smaller 325-tonne slugs at much higher velocities than usually seen, granting it an effective range of almost 200 kilometers; by comparison, most MACs at the time could only reach 90 kilometers. This speed advantage at the time allowed the Halcyon to potential fire twice before their enemy could close in, and in theory allowed it to cripple if not destroyer any one model of destroyer at the time. While somewhat impressive at the time, the rapid scaling up of MAC calibers throughout its production life was such that by the time the last Halcyon was completed, it was already outclassed in all areas by similar systems fitted on frigates half their size.

Acting as its secondary, though far more often used arsenal, only 156 M42 Archer missiles were carried on these cruisers as designed. Far larger than what later models of the Archer line would be, the M42 missile was considered the immediate successor to the fearsome M280 Ares missile, and was similarly specialized for destroying large targets - space stations, starships, small asteroids, and planetary targets. With a fuselage that was roughly seven meters in diameter, these missiles were difficult to carry in numbers on anything but capital ships, and so they were only regularly-seen on battlecruisers and heavy carriers. It was fitted with a high explosive-vacuum enhanced (HE-VE) warhead as standard, but was able to be exchanged with an EMP, decoy, and later ionic payloads for use against energy shielding. They also came in long- and short-ranged configurations, which were fitted according to mission need and whenever it was necessary to squeeze more missiles aboard. These missiles were organized into pods of 26 missiles, with each being fitted with six launch silos, allowing the Halcyon-class to fire up to 36 missiles at once.

An assortment of twelve point defense guns were mounted all around the cruiser's hull, which were designed to act as a last-resort protective measure against incoming missiles and close fighter runs. There were eight M910 Rampart turrets, spaced evenly around the cruiser for maximum coverage. These acted as its primary anti-aircraft deterrence; its four 105mm guns were intended to be used against the heavy strikecraft that entered service before the Insurrection, and their high rate of fire and diverse shells allowed them to saturate the space around the vessel. Four M810 Helix 35mm point defense guns were added to provide extra protection against incoming weapons fire, and were mounted around particularly vulnerable regions - a pair were mounted near the bridge, for example. The Halcyon-class cruiser was one of the last lines of warships to be fitted with the M810 system.

Variants
With the unexpectedly low demand found in the Halcyon-class, RMC took to invest in a number of potential hull upgrades to the class, and experimented in an effort to salvage the insane amount of money they lost developing them. Each of the Halcyon 's variants added an extensive amount of superstructure to the class, with most of it being fitted over the base hull in case the UNSC contracted them to upgrade them to a set standard.

Aegaeon-class carrier
Larger than even the later Autumn-class, the Aegaeon-class carrier is designed around an elongated first flight Halcyon hull, hollowed out to allow it to carry an extended amount of space fighters and material. Produced only in limited numbers, these carriers, like the ships they are built from, never saw extended production. However, the ships that were built went on to earn a mythical status within the fleets they served in.

Measuring nearly than 1,800 meters from fore to aft, the Aegaeon-class still features the same dense honeycomb superstructure which made the base design so durable. However, it does not retain it throughout its entire frame, and incorporated minor concessions in order to make the construction of a larger warship cheaper and thus more feasible. The defensive armaments have been improved and brought up to standards. It still retains a single MAC, but this has been upgraded to a heavier caliber and now runs almost half the length of the carrier, with thirty pods of Archer missiles and dozens of point-defense guns added. While this is nowhere near as powerful as a ship of its size should be, it can now adequately defend itself against more capable threats. Its reactors and engines are larger, although it is still considered slow for its size.