Existing SP-AX 'Sleipnir-type', also known in Imperial service as SP-class, Heavy Destroyers remained a standard unit in the inventory of the incumbent Aquarian Superpower's naval capability for essentially all of the New-Federal Era and beyond, without any major upgrades or enhancements, largely due to more pressing needs of post-Old Federation Navies to develop significantly more capable long-range stand-off vessels, such as the RV-class Fleet Cruiser, and its Imperial Pattern 2 upgrade, the 'RV2M-class' Missile Cruiser.
With the dawn of the 46th Century A.D closing in, the Aquarian Imperial Institute for Naval Research (INR) begin devleopment of an upgrade package for existing SP-class vessels, as per the Imperial Navy's 'New Fleet' upgrade program, initiated by the ATIS Council in 4459 A.D. In large part due to the increasing intensity of the hostilities with the rebel group known as the Eridonia Free Peoples' Fleet, the Imperial Navy found itself committing more and more warships to defensive roles, whereby maintaining a perimeter at medium to close range was emphasised over the long-distance (stand off) ranges of multiple million kilometres envisioned by Imperial Commanders as part of the AIN's overall warfare doctrine.
As such, deployment of the CQC-specialised SP-class Heavy Destroyer increased, and although the class had proven successful against EFPF forces by 4460 A.D, several key areas of concern for a potential upgrade were raised by Imperial Sector Fleets to the INR, who authorised the development of a Pattern-2 upgrade package for all existing SP-class hulls, and all new hulls to are to be built to the Pattern-2 Standard.
The new Pattern-2 vessels have several key changes and enhancements over the older designs. The most notable is the removal of the class's distinctive spinal armament; the twin-linked IMPAC battery was replaced with an upgraded electronic warfare suite, and a third shield modulator with additional, improved capacitor banks. This was achieved in the same mass and only a slight alteration to the prow, by replacing the massive and bulk supercapacitors and charging coils of the IMPAC battery, with the new shield and electronic systems. The reasoning behind this change was due to a tendency for SP-class warships to operate in medium/CQC ranges in the early stage of the Aquarian Civil War, almost always with a fleet-scale deployment including heavier cruisers and capital ships providing long-range firepower.
While highly capable in long-range combat, the SP-class's IMPAC spinal armament was deemed unnecessary for a vessel that had seen itself become a specialised medium/CQC range fighter; operating in screens to protect larger vessels against the faster, more agile frigates and corvettes often employed by the EFPF rebels. As such, the enhanced Broad-Spectrum sensors suite, electronic warfare suite and stronger shields while maintaining the mass budget, was considered a significant upgrade. The SP Pattern-2 has an additional prow-mast antenna for the BSA and SDD systems, along with a new Fire Control System and CIC on the bow upper deck, with a dedicated MLADAR pod for highly accurate target tracking, which was specifically designed to operate in conjunction with the RV-class Fleet Cruiser's long-range IMPAC A-type battery; the effective range of aforementioned battery being vastly greater than the accurate sensor resolution of the cruiser. In this capacity, the SP Pattern-2 is highly effective when operating with Fleet Cruisers or capital ships, and Imperial Naval commanders considered the ability to more accurately direct stand-off fire from supporting cruisers as an effective replacement for the Pattern 1's spinal armament, while affording better electronic systems and shielding at the same time. The ability to operate more effective as part of a fleet requried a designation change from 'Heavy', denoting Heavy Firepower, to 'Fleet' Destroyer; denoting better co-operation with other warships in a fleet environment, such as the RV-class Fleet Cruiser.
Pattern-2 SP-class Destroyers possess a significantly improved drive system. Utilising technology from the RE-II-class Battlecruiser's revolutionary new drive system, the SP Pattern-2 is not only faster at the same mass to its predecessor, but also more manoeuvrable and able to accelerate and deaccelerate quicker, allowing much greater flexibility in combat manoeuvres, befitting a CQC-focused warship. The new drive system, codenamed "STARLIGHT" utilises a new 'phasic slip-stream' capability developed after analysis of the Senlani's own highly capable drive system by Imperial Intelligence Espionage units, "STARLIGHT" was designed directly to counter that technology. It is to be a standard feature on all new upgrades and warship designs used by the Imperial Navy going forward.
The primary turreted main battery of the class has been significantly overhauled with the Pattern-2 upgrade package. In place of the quartet of mid-ships mounted rotary FIMD autocannons, the Pattern-2 is now able to equip the Navy's new HAL3-B (B-type) 'Lance' Heavy Laser Cannons. These improved medium/short-range weapons are able to effectively neutralise frigates and corvettes, along with subsystems on larger warships, due to the vastly upgraded pulse intensity and elongated focusing assembly compared to the existing HAL2 Laser Cannons used on most existing warships. The SP2-class is the first production Imperial Navy warship design to feature the HAL3-B and represents a major progression in offensive laser weaponry. The standard configuration is three, dual-linked 'Lance' cannon B-type turrets, two on the 'shoulders' of the midships section, and one under the prow. These are able to more precisely effect targets than the slower moving kinetic projections of the previous design's Rotary FIMD cannons, and while lacking the space-burst fragmentation capability, more than make up for area of effect with vastly higher accuracy.
Furthermore, the SP2-class is able to mount the Navy's new VIPER missile system turret; the standard configuration is a pair of B-Type mounts on the lower midships section. The VIPER missile system provides effective full-spectrum S/M/R/ELR capability with a variety of configurable payloads and self-contained target tracking. As such, the Pattern-2 SP-class Fleet Destroyer is one of the most heavily armed sub-capital ships in the fleet. The Imperial Navy expects full production of the Pattern-2 hull by 4463 A.D, with full transition of existing warships to Pattern-2 standard by 4470 A.D.