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The UNSC Prevalence, the most known ship of the Impulse-class.
Impulse-class stealth frigate
Production information

SinoViet Heavy Machinery and Vanguard Corporation (Joint collaboration)


Stealth frigate

Technical specifications

510.56 metres (1675.06 ft)


203.57 (667.89 ft)


199.08 metres (653.15 ft)

Engine unit(s)
Slipspace Drive

Mark VII Macedon #4780HDS Shaw-Fujikawa Translight Engine

Power output

Boglin Fields S63/X/DPS Deuterium Fusion Reactor (2)


47 centimetres of Titanium-A battleplate

Targeting systems
Navigation system
  • AI matrix-linked navigation system
  • UNA-linked navigational network
  • 450 crewmen
  • 15 Bridge Officers
  • 250 Foot soldiers and technicians
Minimum crew

1 "Smart" AI

Year introduced
  • 2499 (Initial prototype)
  • 2529 (First deployment)
  • Stealth
  • Fire Support
  • Reconnaissance
  • Exploration
"It was an unusual idea back then, but now, looks like unusual ideas are really what we need at this time of war."
―Gaurav Shankar, the man who proposed the production of the Impulse-class.

The Impulse-class stealth frigate (Hull Classification Symbol: RCB) was a line of heavy frigates used by the UNSC Navy, beginning its service during the initial years of the Human-Covenant War and continuing throughout the Post-War Era. Being on par, but arguably superior to the Paris-class Heavy frigate, the Impulse-class has its main focus on stealth and reconnaissance, making it useful as a scout ship to the UNSC during naval encounters with the Covenant or with the Insurrectionists. It is also extremely similar in design with most of the other SinoViet-manufactured UNSC frigates, sharing almost the same outline and rough look.

Originally prototyped in the last years of the 25th-Century, the Impulse-class featured a midnight-black coating along with various stealth-inducing systems and baffled engines of that time. While the prototype model was effective and did not fail in any technical aspect, it was deemed too expensive and the idea of a stealth frigate was scrapped for decades afterward. However, the design of the frigate was something useful, and it was incorporated into future designs, thus paving the way for SinoViet's traditional frigate look, even though the Impulse-class shares more similarities with the Paris-class frigates than the other classes. Stealth coatings were also under research by SinoViet, although little to no care was given towards it.

After the Covenant attacked humanity in 2525, SinoViet suddenly saw more requests for ships than in the previous years during the Insurrection. This sudden increase in sales also encouraged restarting old projects, mainly the Impulse-class. SinoViet Machinery collaborated with Vanguard Corporation, a private-militia corporation which had its own armory as well as credit for designing a few dropships. The Impulse-class stealth frigate became Vanguard Corporation's first real warship project, and SinoViet's origin model for their frigates finally entered into service in 2529.

The Impulse-class was well-received by the UNSC, with praise being directed towards its special focus on reconnaissance and its versatility as a support ship. While it did not see as widespread use as the other frigates manufactured by SinoViet, it was nevertheless a success, given its limited production and usage, and the names of the UNSC Prevalence and the UNSC Impulse being widely spread across UNSC fleets. The Impulse-class frigates, however, saw extensive use after the Great War, as part of Project JANSZOON, an attempt to expand the colonial space inhabited by humanity, and to explore suitable colony locations before other Phoenix-class colony ships colonized them.

Operational History

Initial Prototype

Near the end of the 25th-century, SinoViet Heavy Machinery was a shipbuilding company, which was primarily known for having designed the Hillsborough-class heavy destroyer, Diligence-class destroyer, and the Nation-class corvette. In addition to these military warships, SinoViet gained much profit from its more diverse range of civilian transport ships, freighters, and carriers. Around the same time, it began facing competition from Reyes-McLees Corporation, which had their first big success with the Mako-class light corvette. Realizing that the RMC was focusing more on experimenting SinoViet pushed towards research and development. SinoViet tried experimenting with a variety of ships, exploring other ship classes too.

One of these ideas became the Impulse-class stealth frigate. While the concept of a frigate was new to SinoViet, instead of trying with a basic one at first, SinoViet decided to test a stealth variant. As such, it would have lesser armor and durability, while exchanging that for speed and firepower. For the design, SinoViet took inspiration from the age-old colony ships that humanity first used to colonize other planets, and put the major focus on the armament. Given the technology at that time, the Impulse-class' stealth properties were nothing major other than being coated midnight-black to decrease visibility and additional systems and upgrades which made the ship less available on the radar, while also sporting a communications jammer.

With the model finishing design and the technology it needed finally acquired/developed, a prototype was created on the blueprints and plans and was put to testing. The prototype proved surprisingly well in a test-run, where it ambushed a group of pirate ships near the Eridanus system, using the element of surprise, and used its comparatively superior armament to take down the ships. The test indeed suggested that the ship was a success, and could be very well the turning point for SinoViet's sales.

However, it experienced an unusual twist; SinoViet's prototype failed to impress the folks at UNSC, who argued that it was expensive for the services provided. They reckoned that in the war against the Insurrection, the UNSC needed more traditional ships, ones that could deliver a good deal of damage to enemy ships while being able to survive on their own during desperate times. The arguably-less armor for a frigate was disliked by the UNSC, and so the prototype failed to enter production. However, the ship's design was praised, and it ended up being the base template for SinoViet's future frigates, for which the company became most notable for, especially the Paris-class heavy frigate. The tested prototype was decommissioned, ultimately being buried in the storage docks in their primary shipyards at Reach.

Reactivation and Production

In 2525, humanity was attacked by the alien mega-theocracy known as "the Covenant". Humanity's first encounter with the aliens was not friendly, and this resulted in the colony world of Harvest being "glassed"; killing all life on the planet and making it uninhabitable, due to the enormously-high temperatures and lack of an atmosphere after it was boiled during the process. After three more ships were sent, the captured footage from the only one that survived the battle and returned to human-space, while being crippled was horrifying and the destruction was very high.

Soon, more of the encounters with the aliens resulted in better understanding of the fact that these aliens were waging nothing short of a great war on humanity. While Dr. Catherine Halsey's SPARTAN-II Project, which was originally conceived to battle insurrectionists proved to be a highly effective method of defense on the ground, the UNSC still needed newer and better warships so that the same level could be maintained in space. Thus, this meant that many of the ideas scrapped by the UNSC long ago could be revived to serve some purpose on the battlefield, whether tactical or strategical. Amongst the few such projects, the Impulse-class was one of the major ones.

While the original prototype which was buried in Reach couldn't be brought back given that it was decommissioned, its parts and engines were stripped for resources, and the original plans for the Impulse were brought back. By then it was indeed obvious that while the original idea was good enough, a lot of new upgrades were required in bringing the ship to modern standards and able to fight the new enemy humanity had. So, technicians were brought and newer upgrades and features were suggested while incorporating the current stealth technology.

This resulted in the real first generation Impulse-class frigates being much technologically advanced than their almost four-decades-old prototype. The Impulse sported the same hull as its prototype, which was extremely similar to the Paris-class heavy frigate, a frigate derived from the Impulse as well. The absolute-black paint was retained, but the disadvantage to it was the paint being worn off on repeated use or on collisions, but nevertheless proved to be an unusual ally in stealth. It also featured a drone that would send short bursts of delayed radar 'pings' to the enemy ship it was fighting, to confuse the ship's targeting systems, and a wide-spectrum flare that the ship would deploy after launching its artillery or when an enemy tries to lock onto it, resulting in the enemy ship's sensors being temporarily overloaded or 'fried'.

But perhaps the biggest change to the ship was a major overhaul of the ship's hull. Instead of the general Titanium-A battle armor plates that are used in most other UNSC ships, the Impulse featured special meta-materials, which specialized in reducing Radar cross-section, scattering the signals away. The entire hull was remade using Split-Ring resonators of various sizes, effectively directing signals to a random point in space and not back towards the transmitter. This was deemed costly, but for a stealth-based ship, the UNSC agreed to have the titanium armor replaced with meta-materials.

In the late years of the war, the UNSC requisitioned three more Impulse-class frigates, this time of the under testing Block II variants. These ships sacrificed some part of the meta-material hull and replaced it with titanium. Instead, these featured larger hangar bays and training simulator areas, causing the ship design to resemble that of the Charon-class light frigate. One of the more notable ships of the Block II Impulse line was the UNSC Mother of Invention, best known for being the mobile command base for the highly-experimental Project FREELANCER.

Post-Covenant War Era

After the Human-Covenant war, the Impulse-class stealth frigate saw more varied use than during the war. With help from the Swords Of Sanghelios in technological advancement, the UNSC gained access to technology far advanced than their own. This tech was reverse-engineered successfully, opening up new possibilities and upgrades to the UNSC's arsenal. Many of the major ship classes in the war were fitted with newly-engineered energy shielding, anti-gravity tech, more efficient reactors and slipspace drives, ship-mounted energy-based weapons, and many more.

First commissioned in 2553, the Block III of the Impulse featured various of these upgrades. The most prominent of these upgrades was the energy shielding, which greatly boosted the ship's self-defense capabilities. It was fitted with many of the Covenant's active camouflage field generators as well. However, the Impulse would see its most-widespread use in Project JANSZOON, a program aimed in expanding the human frontier by colonizing both new and old planets for human settlement. Various of the Block I and Block III ships found their purpose in the program, scouting various star systems for suitable planets before the colony ships terraformed them, while the rest continued their service as warships. A select few, however, were secretly recruited for defense of the planet Argus V while ONI Section Three's Beta-5 Division's fourth generation of the SPARTAN-III Program, Delta Company. They also took helped in ferrying the Delta Company SPARTANs and transporting them to their mission locations, and were probably best known for their involvement in Operation: DARK DESCENT.



Role & Usage

Known UNSC ships