Diligence-class destroyer

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

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.

In the 2480s, the Diligence-class would be reequipped by the CMA Navy to overhaul their weapon systems, as the appearance of titanium-A1 meant that even the Thors were no longer sufficient to guarantee a kill. As a result, their entire missile armament was completely removed, and each pod and silo was replaced with one capable of fitting a single M35 Ares missile, with each being given a reload. This was just enough for saturation salvos at extended ranges, and the monstrous size of the Ares' warhead only required a handful of hits to destroy their opponents. A select number of ships trialed the installation of a single Mark IV Taipan 500mm/38 cal naval coilgun on their bellies, with the results being mixed - although a formidable weapon at closer ranges, the Diligence 's modest reactors could not supply enough power to fire it regularly. The 2480 refit also saw a substantial overhaul of its air defense systems. Six twin turrets of Mark 6 Armstrong naval coilguns, installed so their fields of fire overlapped over the whole ship, were there to engage small cutters and fighters. Meanwhile, four rapid-firing M800 Rampart 40mm quad turrets provided the bulk of anti-fighter and anti-missile defense, which supplemented the existing M655 Vanguard guns. Unfortunately, even after this the ships were still too lightly armed to present a serious threat to modern ships, and were among the first round of ships to be mothballed during the 2490s.

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.

The protection system of the Diligence-class would not be adequately addressed during their 2480 refit, but this would change when they were reactivated for service during the Human-Covenant War. The existing hull scheme was ripped out and replaced with a system that incorporated 800mm of titanium-A1 (later A2) battleplate over the most vital areas. For all its work, the combined structure aimed to stop plasma and kinetic penetration by putting as much mass in the way as possible, as the outdated systems of these ships could not support active cooling of the hull.

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.