In the advent of the Yintaka Conflict caused by orders from the United Vitam State's Executive Council due to some form of foreign mind manipulation, the other known major powers of the star cluster realized the effectiveness of the State's new Harpy-Class Frigate that was used in abundance during that engagement. Were it not for the NIR's use of warp disruption fields and graviton status fields, the State's frigates would prove rather hard to hit with any weapons system aside from anti-destroyer weapons found on most cruisers and all destroyers. The only exception to this were missile launchers used by the Camino Star Empire through trade with the State as well as the Holy Lykan Republic through salvaged State launchers in the past. As the State's Representatives Parliament works to find replacements for the Councilors who have since been hospitalized, the Novus Initium Republic, the Camino Star Empire, the Holy Lykan Republic, and the Liberigi Mandate work to have their ship developers come up with frigates of their own to counter such small craft in the future should they be needed.
In the case of the Novus Initium Republic, it took far longer for Supreme Chancellor Drew to convince the Senate to approve of a fourth warship design after so many centuries of having only three. However, it was decided that in order to cut the cost of the production of such vessels that parts of the Crusader-Class Destroyer would be used in the development of the new frigates. Since the ship would be smaller, their production would take half the time of destroyers meaning that the same cost and amount of resources used to create one destroyer could instead be used to create two frigates. The Senate decided that since the Republic Navy had suffered losses in the number of ships on the front lines in the First Interstellar War that the new frigates would fill those numbers far more quickly.
The developers at Horribilis Industries did not take too long to design such a vessel as they had sketches of multiple concepts during the centennial redesigns back in 5400 AD. One prototype sketch, designated "Small-03," was used as a base for the eventual design of the Crusader Destroyers long ago. They looked over the design once more, improved and updated the overall layout of the vessel with up-to-date equipment, and quickly constructed a prototype within a few months. Initial tests of the prototype showed that the number of engines allowed the vessel to be one of the fastest ships in the known cluster with eight sublight engines. This also allowed the vessel to achieve warp speeds faster than any vessel as well. However, this speed came at the cost of a lot of energy and thus ship commanding officers would only use that speed in an emergency or in combat to circle an enemy. Despite the ship being larger than the State's Harpy, the ship's speed and maneuverability were still on par if not better by comparison.
Much of the overall size of the frigate was due in part to the continued need to be survive in combat while remaining a viable combatant. This meant that the ships shields, shield boosters, and armor repairer systems as well as the eight overall laser turrets had to have sufficient power to run it all. The size of the prototype allows it to have enough room on board for the needed number of reactors to make that possible. However, the room needed and the size of the vessel also came at a cost. The accommodations and the amenities aboard the prototype were spartan in general and would feel more like a warship. Only officers had larger quarters and even then they were sharing them with another officer while the only exception is the executive and commanding officers. This also meant that the ship could not be out on patrols away from port for prolonged periods of time due to the sizes of their available cargo holds.
The design was eventually brought forth before the Senate, the Joint Chiefs, and the Supreme Chancellor for review. While some in the military complained about the design and the sacrifices made to achieve the desired results, the design was eventually approved for production by the Senate and was given the proper title of the new Sentinel-Class Frigates.
With the introduction of the Sentinel-Class Frigates, the restructuring of commanding officer requirements for different classes of ships had changed, much to the dismay of those affected. The highest rank to command the Sentinels now is still Lieutenant Commander, the lowest rank meant to command Crusader Destroyers in the past. Those up for promotion to that rank found themselves in command of a Sentinel instead of Crusader, causing a lot of tensions and issues. Several Lieutenant Commanders already in command of a Crusader Destroyer, however, found themselves being promoted to the rank of Commander, the new rank to command destroyers, in order to continue commanding their assigned vessels. This restructuring has already given the Sentinel a bad reputation among the military of the Republic Navy, though some are quickly realizing that they are in command of a very nimble "dog-fighter" of a ship that can easily run circles around larger ships. Military analysts believe it will be some time before the Sentinel will be in favor with the lower ranks of the military, though this may change once commanding officers and their crews realize the true combat capabilities of the new frigates.