The HS-225 Tengu was the first and last production-model Variable Exo-Frame used by the Ohkan Union of Prosperity. Developed in secret, its appearance proved to be a shock to the Astralan Federation, who belived they had a monopoly on Variable Frame technology.
Developed from a series of developmental frames (the details of which have long been lost to the ravages of war), the Tengu was devised as a mass-production worthy frame that would be able to go head-to-head with the Astralan VEF-04A Hawk. The development team was tasked with creating a machine that would be equal to or excelling the Hawk in key aspects of speed, maneuverability and acceleration. The craft's armament was considered a secondary goal to these factors.
Imperial Aerospace Research started with the IAR Model 40 Fusion Turbines from the excellent HS-200 Hien, considered to be the best engines available to them. These were incorporated into a new frame which combined elements from the Hawk and the older VEF-01A, but refined and optimised for greater agility. Initial tests compared favorably to the Hawk, the new aircraft demonstrating superior agility and superior speeds at lower altitudes.
However, in order to achieve these aims, IAR took a number of shortcuts which, while considered acceptable at the time, would later come back to haunt the design. While the weapons load was considered adequate, the HS-225 lacked the Hawk's heavy beam cannons, giving it less direct firepower. Similarly, while it had four underling hard points, they were rated for lighter maximum loads. Likewise, the designers cut back on the overall armour protection of the craft, making it somewhat more vulnerable to enemy fire.
Despite this, the Tengu's performance was considered to be well above requirements; pilots were expected to use their superior agility to overcome their foes' advantages in weapons and protection. Furthermore, to many, the Tengu was seen as an interim design to be mass-deployed until the Union could develop a newer, more powerful frame.
Exactly how the Okhans acquired variable frame technology is unclear; both the secrecy of the project and the destruction of the Union at the war's end meant that, to this day, very little information it available on the early development and service of the craft. It is known that the fighter first entered service around 3165, equipping frontline squadrons. Used in their initial attacks on the Federation, their very presence caught the Astralan pilots by surprise, allowing them an unexpected degree of success. As a result, the Federations' pilots needed to develop completely new tactics to deal with this unexpected threat.
In combat, the Tengu proved to be a rough equal to the Hawk; the pros and cons of each fighter roughly balanced each other out, with matters of pilot skill and tactical support more often proving to be the decisive factor between the two craft. While the Hawk was available in greater numbers, the division of the Astralan forces between the Okhan and Brasniayn fronts meant that there were only so many craft that could be deployed at any one time, especially after the revelation of the As-35A Valkyrie.
However, the adaptable Astralan pilots began to develop ways to work around their foes; preferred tactics were to turn dogfights into head-on slashing matches which gave the advantage to the more heavily armed and armored fighters. And while less agile then the Tengu, the Hawk's better acceleration and rate of climb meant that a canny pilot could drag the Tengu into a situation that better favoured them. The Okhan pilots in turn tried to adapt, resulting in a continual revision of tactics.
Two factors changed matters to the Astralan advantage, however. The sudden end of the Brasniyan war meant that a large number of craft were redeployed to the Okhan front, resulting in the Tengus fighting at a sudden numerical disadvantage. The second was even more alarming, with the arrival of the VEF-08A Raven, a craft that matched or excelled the Tengu in every way. Suddenly, the Okhan pilots were fighting at a severe disadvantage and being slaughtered in the air.
In response, the Okhan military began a crash program to develop a better fighter. Unfortunately, even at the best of times, the Tengu's replacement, the proposed HS-250 Raiden was years away from production. As an interim, several sub-variants of Tengu were developed as a way of addressing the craft's deficiencies; while partially successful, none of these variants were able to make up the considerable performance gap the Tengu was suffering.
As a result, the Tengu would remain in frontline service until the end of the war. The last operational squadrons fought to the bitter end, often seeing handfuls of fighters facing off against skies full of Astralan Ravens. Post-war, the handful of survivors were junked, with only a few preserved.
- HS-225T Tengu - Twin-seat trainer model
- HS-225M Tengu - Advanced model; added extra armour to the fuselage/torso and wings, as well as improving the carriage capacity of the hardpoints and slightly improved the performance of the engines; extra power was insufficient to offset increased weight, however. Mass-produced for the last year of the war, but never replaced the base model.
- HS-225MK Tengu - Improved M model with addtional Tanegashima Model 65 Beam Cannons in the wing roots. Extra weight and power requirements degraded performance even further. Only produced in limited numbers.
- HS-225Kai Tengu - Further improved M model using weapons and systems from HS-250 project, resulting in overall performance improvement. Only three prototypes built, all lost in combat.