Diligence-class destroyer

The Diligence-class was a high-endurance patrol ship commissioned for use by the CMA.

Role
As with the other vessels also retroactively referred to as "patrol cruisers", the Diligence-class was specifically optimized towards patrolling the undeveloped Outer Colonies. This mission set was extraordinarily challenging, as stations able to resupply CMA ships were few and far between, it was difficult to coordinate ships even if they were operating in the same sector, and intelligence was often spotty at best. As a result, they were particularly good at scouting and independent operation, but were armed only well enough to destroy low-threat opponents and provide a deterrence value to stationary targets. They had the basic facilities to act as a flagship for small flotilla and ground control operations, but for a sustained conflict this was only an interim solution until a carrier could be deployed to the theater.

In a CMA fleet environment, the unrefitted and refitted Diligence served two different roles. The unaltered ships acted as frigates, either scouting for the main force or keeping a close escort for the flagship. The refitted vessels functioned as destroyer leaders, supporting smaller ships with their superior Ares armament and taking command of small force detachments where necessary.

Under UNSC service, the Diligence were relegated to destroyer and auxiliary roles. In fleet engagements they acted as fire support ships, lobbing missiles and MACs from a distance, as even in their refitted state they could trade blows with Covenant warships. It was more common for these ships to take over second-line duties to free up more modern frigates and destroyers for action. They served as convoy escorts where their somewhat slow speeds were a benefit, and the freed-up space in their hull made them excellent troop transports for their size. Perhaps more notably, Diligence-class destroyers were later updated to enhance their anti-fighter, anti-plasma torpedo, and countermeasure systems, where they continued to protect nearby ships from harm.

Armament
The armament of the Diligence-class varied considerably over the course of their operational lives. Their initial armament was quite conservative, split between 30 pods of M31 Loki missiles which were backed up by ten far heavier M19 Thor ballistic cruise missiles, both of which were fully suitable to the long-ranged battles of the day. The M19 Thors were anti-shipping and ground attack weapons designed only for utterly annihilating targets with no chance for rescue, and represented the most powerful weapons regularly carried by these ships. Somewhat strangely, it was the lighter M31 that saw far more use. Built with underpowered warheads, the Lokis were incredibly agile, and allowed them to excel in disabling enemy ships by taking out their vital systems. This was important because during this time, there was a strong moral disincentive to outright destroy craft with all hands, and indeed it was common for the victors to engage in the search-and-rescue of enemy crews. For point defense, a suite of 14 single M655 Vanguard 20mm/35 cal point defense guns protected them from incoming missiles and strikecraft, using their small, high-velocity shells to reach out at a considerable distance.

Protection
The initial protection scheme of the Diligence-class cruisers differs considerably to that of later vessels. While later human warships would be covered with thick plates of titanium-A battleplate, the Diligence only had thin plates of grapheel protecting vital areas such as the bridge, ammunition bays, and the machinery spaces surrounding the fusion reactor. This was because that it had been recognized that armor could only protect the ship against lighter point defense gun fire at relatively close ranges. Medium anti-shipping missiles, let alone the nuclear-armed cruise missiles, could easily blast through any thickness of grapheel that stood in its way. As a result, the hull had been designed to mitigate damage inflicted rather than resist it, with an extensive series of blast doors, redundant systems, and a spaced double-hull configuration. The actual protection had to be provided by countermeasure and decoy launchers and point defense guns aimed at either intercepting or dodging hits completely. Although this combination was considered effective during the Pax Humana, especially given the difficulty of procuring sufficient numbers of naval armaments during the period, the escalating size and capability of missiles during the Cold War - and the shortening engagement ranges made possible by more advanced slipspace drives - would make the Diligence-class particularly vulnerable in any new conflict.

Embarked forces
The modest force the Diligence-class carried was heavily weighted towards infantry and aircraft, with only a small armored element being present. There were accommodations for up to one hundred CMA Marines - enough for two platoons. Unlike their UNSC counterparts, the CMA Marines were generally used for small team operations, such as investigating derelict ships or performing commando raids on hostile elements. They were, nevertheless, trained for conventional engagements. Armored support consisted solely of a platoon of M12 Warthog FAVs.

The Marines relied on the airwing to make up for their lack of ground punch, which had been partially informed both by the Marines' need for mobile support over large distances and the CMA's experiences during the Inner Colony Wars. There were a total of 12 aircraft ready to support them, divided between gunships, VTOLs, and fixed-wing fighters. All of them required some capacity of orbital flight in order to reach the surface, as the Diligence was in no way capable of atmospheric flight. Three D56-TC Hurricane dropships would deploy the Marines and Warthogs to the surface. Unlike the later varieties of Pelicans, the Raptors only had an enclosed bay to carry troops and material, and their total carry weight was also much more limited. The Diligence could coordinate all ground operations from a D4 Lada command-and-control orbital lifter, which normally remained attached to the ship but could be deployed to command troops on the surface. As a lifter rather than a dropship, its descent was long, slow, and vulnerable to anti-air fire.

In addition to these, two small space fighters were carried for both point defense and scouting purposes, expanding the ship's scout radius without putting it directly at risk.

Operational History
Commissioned into service during the 2430s as a cruiser, the Diligence-class had a long, proud career as peacekeeping ships. Although some were kept back to act as escorts for the CMA's carrier fleet, the vast majority made long tours across the expanse that was the Outer Colonies, usually traveling alone in order to cover the widest area of space possible. Many of their patrols were often so remote that they that their were often the only point of contact made between the colonists and the UEG. To this end, their crews played a large role in settling colonial disputes - some of which were overturned by the CMA and UNSC command staff when they felt the resolutions weren't in their best interests.

As the Cold War tensions escalated and drove military development, it was becoming clear that the Diligence-class was showing its age. While still useful for patrol, the introduction of cruisers magnitudes heavier and far more capable than these humble vessels pushed them far away from combat roles. As a result, although they received a modernization in the 2480s to keep them competitive, the entire class was mothballed during the 2490s as the UEG began to clamp down on the CMA's budget.

When the Covenant War erupted in 2525, all assets of the CMA were forcibly absorbed into the UNSC, and this included their collection of outdated ships in their reserve fleets. The fates of these ships varied - those that were too worn out were simply scrapped, while those in good-enough shape were given a modernization that saw a substantial upgrade of their electrical, protection, and weapon systems. They served in numerous different positions, with some directly fighting the Covenant in often-suicidal holding actions, while others were held back to escort civilian convoys or act as troop transports. As the war went on, the demand for air defense ships meant that most of the survivors would sport significant numbers of point defense guns and Streak anti-fighter missiles. The class would survive the extinction of most CMA ship classes through the 2530s, but those in UNSC service would not survive the war, with the last UNSC-controlled Diligence, the UNSC Valkyrie, being lost in 2547.