In 4459 A.D, the Aquarian Imperial Navy iniated the Fleet Rearmament program; whereby the Admiralty expressed a requirement to update the Fleet's arsenal with newer, post-Imperial Era designs built to address matters of security and conflict within Aquarius and beyond, going forward. The program would include extensive upgrade packages for existing hulls and several, completely new, hull designs built to operate the Navy's latest and most advanced weapon systems just entering service at the time. One of the new hull designs was the TH-type, or 'Thunderhead-class' Heavy Cruiser - a vessel designed to bridge the gap between the fast RV-type Fleet Cruiser and the larger ED-type and RE-II-type Battlecruisers.
Such a warship would historically fall into the Heavy Cruiser classification (CCH); once the workhorse of Aquarius's military power, but largely fallen out of favour in the post-Old Federal Era navies of the cluster, in part due to the advancement of weapons capabilities on smaller, faster ships such as the RV-type and SP-type medium and light cruisers. Historical classifications of CCH include the Vengeance-class; which had an extensive and well decorated service career with the Old Federal Navy, and remains in service to this day with various independent factions throughout Aquarius due to the sheer number that were built by the Old Federation.
The Imperial Navy inherited a large number of Vengeance-class CCH hulls from the UAS during the transition to the Imperial Era in 4402 A.D, which themselves (being VE-AX type cruisers) were inherited directly from the TLA and the remnants of the UTN's last few heavy cruiser fleets after the Fall in 4040 A.D. These ancient warships were slowly being phased out in UAS service in favour of the pre-imperial version of the RT-type, the Revolution-class Fleet Cruiser, which continued in Imperial Service, although a few Vengeance-class CCH hulls did remain in service as the VN-type Heavy Cruiser well into the 46th century.
The requirement for a Heavy Cruiser was put forward by the Imperial Naval Strategic Analysis Commission in 4462 A.D after Operation Ultima in the Angel Hook Nebula against the EFPF rebellion. It was considered important that the Fleet possessed a fast but heavier armed and armoured warship that could provide Battlecruiser (CB) class defensive capability and to a lesser extent, armament, but with a mass low enough to perform fast manoeuvres with fast cruiser groups, including the Navy's highly successfully RV-type fleet cruisers, and SP-type destroyer/light cruisers.
Existing heavy warships of the Capital class such as the ED-type Battlecruiser, itself based on a hull design nearly a thousand cycles old, were simply too heavy to conduct fast raids whereby warships are expected, and required, to perform very sudden course-alterations without significant prior notice. Though the Navy's new RE-II-type battlecruiser possesses incredible speed for a CB-class warship, the vessel's mobility is impaired largely by the much larger mass and sheer size of the battlecruiser classification.
In order to address the requirement for a defensive-focused 'fast warship', the Imperial Institute for Naval Research began experimenting with a new class of warship with a specific mass envelope and weight-to-thrust ratio, incorporating new advances in Gravimetric Gyro and Slipstream Drive Technology to allow a much heavier warship than the RV-type to perform similar manoeuvres, thus providing fast-cruiser groups with an effective, defensive-oriented M/CQC ship-of-the-line.
The result of a decade of engineering design, the fruits of the project produce the TH-type Heavy Cruiser, also known in the Imperial Navy Register as the 'Thunderhead-class'.
The new warship features a unique structural design with an optimised centre-of-gravity and mass signature, powerful Slipstream Drives based on the Navy's new 'STARLIGHT' drive technology that had been incorporated on the SP-type Pattern 2 (SP2) and RE-II-type battlecruisers already in service with the fleet. The result was a warship with incredible acceleration, deacceleration and turning capability but with a mass budget large enough to incorporate much heavier powerplants required to operate battlecruiser-level shielding systems and weapons supercapacitors.
Although the Thunderhead-class's main battery is no larger than the RV-type Fleet Cruiser, with only two A-type hardpoints, it possess an extensive secondary armament with 8 B-type hardpoints, and significantly increased frontal and side armour protection, powerplants and shield generators. The emphasis of the Thunderhead-class was to protect Fast Cruisers from interdictor cruisers or capital ships in medium to close quarters engagements in fleet-scale warfare. As such, the warship is optimised for ship-of-the-line duties at the expense of long-range stand-off firepower.
The increased mass budget of the CCH classification allowed Imperial Draughtsmen to incorporate a hangar facility with a utility bay for gunship-type strikecraft and an extensive internal flight deck for DF430 Multi-role Starfighters; allowing Thunderhead to deploy a respectable contingent of strikecraft wings to assist it in protecting the fleet's more vulnerable fast cruisers from bomber harassment.
Armour protection is focused around the frontal arc of the warship, with minimal additional main-belt protection on the ship's stern, the result is a warship that emphasises frontal and front-side assault on enemy capital ships or cruisers, but with significantly increased shield protection for the more vulnerable rear section. The design is a trade-off to allow heavier frontal arc protection within the strict mass budgets of the CCH design.
TH-type warships completed their first field trials in 4470 A.D, and the Navy has requested full product of the new class by 4475 A.D, with combat readiness of at least a dozen full-strength Task Force-scale deployments by 4480 A.D. As such the TH-type Heavy Cruiser is set to become the new backbone of the Imperial Navy's 'fast heavy strike' capability, replacing the older Vengeance-class as a ship-of-the-line; the first such designation for nearly a thousand Terran cycles.