F-350 Scimitar

The Covies had landed on Seraphis III, but apparently they hadn't seen us yet. We popped a couple of those fancy countermeasure rockets, then flew over their drop zone unnoticed and emptied a pair of 2000 liter tanks of fluoroanti-whatsit acid on their base. They were off the planet the next day. Apparently half of the Brutes had died from drinking the water. -Unknown UNSC Pilot
The F-350 Scimitar was a fighter designed after the Great War as an air superiority fighter. It utilized several new technologies developed during the war, as well as a few older ideas updated with new technology. Overall, its high maneuverability, endurance, and payload made it an extremely effective fighter, though its inability to perform trans-orbital maneuvers made it somewhat difficult to recover.
==Development==
After the Great War, it became clear that the current human fighters were woefully ineffective against Covenant aircraft. While Hornets could typically handle Banshees in one on one fights, they were usually outnumbered, which made them far less effective, and they stood almost no chance against the much faster and better armed Seraphs, which would achieve extremely high kill ratios against any UNSC aerial systems. It became clear that the UNSC needed a new fighter system, one that could defeat or at least match the Seraph in a one on one fight. While several concepts were proposed during the war, it wasn't until after the war that humanity was able to develop any of them. 
Of the concepts proposed, most were reminiscent of 21st and 22nd century air superiority fighters, as there had been no conflicts requiring dogfighting craft since then. Several of them, in fact, were simply versions of those fighters updated with newer materials and electronics. All of these designs were modeled extensively on computers, and while all were found to be effective against Banshees, most were found to be highly ineffective against faster craft. A few, however, stood out from the others as much more effective aircraft, and were built as prototypes.
==Prototype Stage==
Three prototypes were built. The first was a highly maneuverable, well armed and armored aircraft with a limited range, and was rejected due to its lack of loitering ability, but was adopted for limited use as a short range interceptor. It was later modified with spacecraft grade engines and fuel, and was found to be extremely useful as a spaceborne fighter. However, since the aircraft would need to be able to stay over the battlefield at least as long as the Seraph in aircraft form, it was eventually rejected.
The second was also maneuverable, well armored, and had a longer range, but was rejected due to a lack of onboard weaponry. While it could loiter for a long time, this vastly reduced its armament capabilities, to the point that it was believed that a skilled Seraph pilot could destroy one in a dogfight about 50% of the time. While this was sufficient to be selected for prototyping, in light of the performance of the other prototypes, it was rejected.
The third prototype, however, was far more successful. It was not quite as well armed or armored as the first prototype, but it had a much longer loitering time either of the other prototypes, and was deemed to have sufficient performance to engage and defeat multiple Seraphs in a dogfight. It eventually moved on to the next phase, and an experimental variant was developed.
==Experimental Stage==
The aircraft was most notable for its nuclear engines, which provided it with both extremely long range and thrust. The concept was based on a concept that had been toyed with since the mid 20th century, but never put into practice. A nuclear engine was essentially a standard aircraft that contained a nuclear reactor that vented as much as possible of the heat produced by the nuclear reaction into the air fed into the engine. The original concept had used a fission reactor that was virtually unarmored, and leaked radiation into the surrounding atmosphere as well as the engine. It also carried large amounts of radioactive nuclear fuel onboard, meaning that problems with the reactor could result in an unshielded meltdown. Additionally, a crash would result in the reactor scattering large amounts of radioactive material around the crash site, which was usually quite inconvenient to the humans living in that area. 
All three problems were easily fixed with the application of newer technologies. The highly dangerous fission reactors were replaced with safer fusion reactors about the size of a UNSC Marine's fusion pack. These fusion reactors had their standard protection on their external facing sides, and an infrared transparent layer facing inwards to vent the heat into the engine. The fusion reactors came pre-shielded with shielding considered sufficient to keep Marines safe at close quarters, and as such, the aircraft required no additional shielding. Additionally, the fusion reactors contained no radioactive material, and could not meltdown, so there was no worry about crashes scattering nuclear material around the crash site. Due to the size of fusion packs, the engine was also able to carry 8 reactors in each engine, meaning that the failure of any given reactor was not a serious problem, and only resulted in a slight reduction in performance. These engines also did not require an atmosphere that contained oxygen. While lower specific heat atmospheres provided more thrust, the difference was not large enough that it had a noticeable impact on performance. 
The main downside of the nuclear engines was the fact that they did not use onboard propellant to fly, and therefore could not achieve orbit, as there was not sufficient atmosphere in space to develop significant thrust. The aircraft was modified with a system that allowed one of the weapon bays to be loaded with a tank of reaction mass, which could be fed into the engines to allow the aircraft to reach orbit. However, this meant that the aircraft was deprived of a weapons bay, meaning that it was less effective at combat, and would often be destroyed by Seraphs without achieving a single kill. However, it was not intended for use as a space fighter, so the aircraft was put into production rapidly.
==Integration in to Service==
The production stage was if anything, smoother than the prototype stage. After a few initial complications with contractors, the production phase went remarkably smoothly, and were built rather rapidly. Actually integrating them into the fleet proved slightly more difficult, but only slightly. An ablative heat shield was designed to fit over the aircraft and shield it from the heat of re-entry, slow it down, then fall away to allow it to simply drop into an air to air battle, though it usually carried at least one tank of reaction mass during an orbital drop, so its air to air capabilities were limited. 
However, once it reached the ground, it was a huge success. Pilots were routinely able to destroy 3 Seraphs in a single battle, due to the Seraph's lack of a long range guided weapon. While in dogfights, the ratios were closer to even, due to the Seraph's more powerful shields. However, the Scimitar's better maneuverability made up for this, as did its guided missiles.
==Airframe==
The airframe itself was designed for higher heat tolerance over shockwave resistance, as the convenant mostly used plasma based weapons, and with its higher maneuverability, the aircraft could easily dodge slow moving fuel rod blasts. The aircraft's outer skin layer was composed of a thin coating of carbon fiber reinforced carbon, which gave the aircraft a high resistance against the thermal shock caused by an impacting plasma bolt. It also had a relatively low thermal expansion coefficient, which meant that events such as reentry and impacting plasma bolts didn't cause significant damage to the aircraft's aerodynamic characteristics. The inner layer was mainly composed of a beryllium-nickel alloy sandwiched with lattices of carbon nanotubes for additional armoring effectiveness. Beryllium's high specific heat capacity, as well as its hardness and corrosion resistance when alloyed with nickel, which had a high melting point, gave it very good protective capabilities against Covenant plasma weapons. While it could not simply dissipate an aircraft grade plasma bolt, it mitigated the damage each bolt caused, and allowed the aircraft to survive repeated strikes by plasma bolts that would do significant damage to standard aircraft. The F-350, unlike many previous aircraft, did not have a true canopy. While it did have the noticeable cockpit bubble seen on most fighter aircraft, it displayed the surroundings on internal screens, giving the same visibility that pilots would normally get, but without the added weakness of the transparent canopy. Additionally, the screens allowed pilots to zoom in on targets or display data about them on the seen image rather than requiring a Heads-Up-Display or helmet mounted screen to do so. The fusion packs themselves were armored as best as possible, with their own weak shielding system and extremely thin layers of superdense Ceramic-Titanium armor sandwiched between layers of beryllium to provide effective protection. Each engine had a single double layer of superdense Ceramic-Titanium armor under a much thicker layer of beryllium and carbon fiber reinforced carbon. 
Below these armoring layers was a layer of superinsulating silica nanofoam aerogel designed to keep any heat that got through the armor from affecting the internal systems. The aerogel was chemically treated to be hydrophobic, preventing it from absorbing any water that wound up inside the aircraft, which could potentially damage it. This aerogel was incredibly effective, and was actually lighter than air, reducing the weight of the aircraft. The engines were surrounded with a two inch thick layer of the gel to prevent heat leakage to the rest of the aircraft. 
The next level of armor was a faraday cage through which antennae could be extended and retracted to protect them from EMPs in the case of a nearby nuclear detonation. The onboard radar system had its own faraday cage which could be closed to prevent damage from stray signals while the radar was not in use. This faraday cage was composed of a room temperature superconductor, which theoretically gave it infinite effectiveness, though in practice, nearby EMPs could cause damage to the superconductive layer, though an EMP that nearby was usually accompanied by a nuclear blast capable of knocking the aircraft out of the air if not vaporizing it. 
Inside this layer was a layer of what was essentially a fabric made of carbon nanotubes to catch any pieces of the armor should something penetrate the armor all the way through. This was something of a last resort, as the number of plasma bolts needed to penetrate the rest of the armor meant that if plasma bolts were hitting internal systems, despite its robustness, the aircraft was probably not going to survive anyway. 
The wings were generally swept forward 30 degrees, though they could be swept backwards to trade maneuverability for speed. The aircraft included supercritical airfoils, which reduced drag, increasing speed, and giving the aircraft a longer range. Unfortunately, while these airfoils reduced drag, if airflow over the airfoils was lost, the aircraft was limited to purely thrust vectoring maneuvers, which meant that the aircraft essentially had to hover in order to regain airflow over the wings. The wings also contained polymers that expanded and contract with the application of an electric current, enabling the aircraft to better control airflow over the wings, increasing drag over the wings to increase maneuverability or decreasing drag to increase speed. The aircraft also had canards just forward of the wings, which were controlled by omnidirectional geared motors, enabling the aircraft to better control its flight, be it tightening its turn radius, increasing flight speed, or just enabling it to perform acrobatics it would otherwise be unable to perform.
==Propulsion==
The engines sat on either side of the aircraft, and had adaptable intakes to allow functioning at any speed up to Mach 7, depending on the atmospheric density. At speeds up to about Mach 1.5, the engines functioned as turbofan engines. In turbofan mode, the engines generated about 40000lbf (178kN) of thrust, allowing the aircraft to supercruise, though this was a misnomer, as the engines didn't have afterburners. At about Mach 1.5, the fan blades retracted into the air intake spike, which extended slightly to allow the shape of the intake to naturally compress the incoming air, which vastly decreased drag, allowing it to reach speeds of up to Mach 5. In this mode, it generated about 70000lbf (311.5kN) of thrust, but the drag from the ramjets prevented the aircraft from reaching its top speed. At about Mach 5, the engines changed shape yet again, turning the engines into scramjets. At this point, the engines reached their maximum thrust of 80000 lbf(356kN), and with the minimized drag of the scramjet intakes, the aircraft reached its maximum speed of Mach 7. With onboard reaction mass, usually oils due to their low specific heats and masses, it could achieve velocities of up to Mach 11 in the atmosphere and Mach 25 on an exoatmospheric flight path. The engines had three dimensional thrust vectoring capability, giving higher maneuverability, and allowing it to take off and land vertically when carrying a light to medium load, and giving it short takeoff capability with heavier loads. These engines enabled the aircraft to outspeed and outmaneuver Seraphs, giving it much better dogfighting capabilities. With its nuclear fueled engines, the F-350 could remain on station for nearly as long as the Seraph, as long as it didn't run out of onboard munitions.
==Power==
The aircraft contained 12 standard marine Fusion packs in a heavily armored mounting just behind the cockpit. Four of the packs were devoted solely to the aircraft's shielding system, which gave them shielding that was weaker than the Seraph's, but powerful enough to allow them to survive a few point blank hits from the Seraph's cannons and still shoot back. Two of the fusion packs were dedicated to the aircraft's W/AV M6 G/GNR, also known as a Spartan Laser, giving it extremely short charge up times, while a highly efficient Sisyphus cooling system, powered by an additional fusion pack, gave the Spartan Laser a cycling time of about a half a second, though it was rarely fired that quickly due to the risk of running out of power for the fusion packs, which gave about 400 shots total before depletion. The fusion pack used for cooling powered an additional cooling system for the M334 Xyphos, and an additional fusion pack was used to power the Xyphos itself. Two of the fusion packs were used to power the aircraft's avionics. The two remaining fusion packs were held as backups, and could be used to allow the shields to recharge more quickly, or to give the Spartan laser a few more shots should it exhaust some of its fusion packs. While these fusion packs were rarely required, they proved extremely useful when they did become necessary.
==Sensor Systems==
The aircraft had a fusion powered Actively Scanned Electronic Array, which could detect large Covenant aircraft such as Phantoms from ranges of up to 500km, and could accurately detect Seraphs and Banshees at ranges of up to 300km. The radar could even focus onto targets to jam their radars, or at extremely close range, usually under 2km, could damage electrical systems, or even fry the pilots of the enemy craft, though the aircraft lost most of its tracking capabilities when it resorted to this tactic, known as "beaming," This worked because the radar was composed of 1500 small beam/receiver modules, which could be focused on a single target to hit it with a much more focused beam of radio waves, which disrupted electrical systems and even cells at close range, while at long range the sheer power of the radio waves could overwhelm enemy radars.
The aircraft also had an infrared search and tracking system, which could detect and track Seraphs and Banshees at surprisingly long ranges, in some cases up to 600km in a tail chase due to the sheer heat of the Seraph's plasma exhaust, nearly comparable to the heat from the launch of a Shiva missile. This was due to the fact that the Covenant didn't use infrared scanning systems, and thus didn't bother to protect their ships against detection by such systems. The system was sensitive enough to detect a plasma pistol shot from 5km, though at that distance, it could not really give precise vectors, only a general area in which the shot was fired. This enabled the F-350 to effectively track targets from long range without being detected. The system could even track targets in Active Camouflage at close range, which enabled it to act as infantry support at low altitudes.
==Countermeasures==
The F-350 contained a standard suite of countermeasures, as well as some more exotic ones created based on lessons learned during the Human-Covenant War. It contained the standard jammers, trackbreakers, and other such such electronic countermeasures, which were fairly useful in defeating standard Covenant sensor equipment, but there was one sensor that the humans had only been able to defeat once: The Luminary. However, that one time proved incredibly useful to the humans, who were able to use that single decoy design, along with the Luminaries on captured Covenant ships, humans were able to determine that the Luminary used an entirely unknown method to track the bioelectric field generated by humans, and could thus display the Reclaimer symbol. The F-350 contained 25 extremely small rockets capable of generating the same field as a human, thus fooling the Luminary into displaying a Reclaimer symbol over the decoy, while a similar technology was used to prevent the Luminary from detecting the pilot and weapons systems officer should they happen to be onboard. The rockets could be tuned to emit the signals of a Monitor, which would often be enough to decoy away an entire squadron. These rockets had extremely small explosive charges onboard, and would self destruct rather than allowing the Covenant to discover that they were decoys.
The F-350 also had its own shielding system produced by 4 Fusion Packs, giving it even greater resistance to fire than similarly armored aircraft. The shield was fairly durable, and could deflect extended bursts of plasma fire, but was not as powerful as the Seraph's shielding. However, due to the backup Fusion packs onboard, the shields could recharge incredibly quickly, and the aircraft was still adequately protected from enemy fire. The shields also assisted during orbital drops, and while the heat buildup usually broke through the shields, they prevented the aircraft from experiencing the full heat of the drop.
==Weapons Systems==
The F-350 contained some of the most advanced weapons available to the UNSC. The most basic was a fusion powered Spartan Laser. The fusion power source gave it a remarkably quick charge up time, and the Sisyphus cooling system enabled it to cool down even more quickly, the result being a Spartan Laser that could fire about a burst every two seconds. The laser had an added lens that could deflect the beam by about 5 degrees, which made it much easier to use in a dogfight, since it didn't require the aircraft to keep its nose pointed at the target constantly in order to fire. With a well targeted burst, under clear conditions, the laser could destroy or disable a Seraph at ranges of up to 50 km, and could destroy Banshees at nearly 150km. It could also knock down a Seraph's shields at ranges of up to 75km, which would allow other aircraft to destroy them without having to deal with their shields. The Spartan Laser was also modified with a separate mode which fired a microwave laser instead of the standard red laser, which, while it reduced the laser's range, enabled the aircraft to destroy electronics at long ranges, and a microwave laser burst at 75km was usually enough to inhibit a Seraph, if not disable it entirely.
For closer range fighting, the F-350 had a more advanced weapon system than even the Spartan Laser. Upon the Chief's return to Earth after destroying the Unyielding Heirophant, the data Cortana had recovered on Covenant plasma cannons was transmitted to scientists already tasked with understanding the inner workings of Covenant plasma weapons. The resultant project produced a weapon capable of firing a second long blade of plasma at 50,000 meters per second, but it required two seconds to cool down even with advanced cooling systems. At this point, the project would have been canceled, but one of the scientists had the idea to set up the system like a gatling gun. The result was a 6-barrel weapon system that could fire a half second burst from each barrel, but was still able to give each barrel the two second cool down time it required. The system was as effective against small ships as the large scale system had been against capital ships though at much closer ranges. The Xyphos could tear a Seraph to pieces at ranges of up to 15km, and could take apart formations of Banshees at up to 20km. It was fusion powered, which gave it a practically unlimited number of bursts.
For longer range fights, the F-350 had AIM-273 Sniper Advanced Multipurpose Missiles. The Sniper was by far the most advanced air to air missile ever created by humans. It contained a fusion pack about the size of the Fusion pack used in MJOLNIR, and output about the same amount of power, but would only last about 20-30 minutes at full power. This still gave the missile a range previously only thought of in cruise missiles. These missiles could achieve a top speed of about Mach 5 under normal circumstances, and could easily outmaneuver Seraphs. The missile, once launched, ignited its first stage rocket motor, accelerating it to about Mach 0.5, at which point its nuclear ramjet kicked in, quickly accelerating it to Mach 5. The fusion reactor gave it a range of about 1500km, and its velocity meant that it could be used against ground targets as well as aircraft. It had built in millimeter wave rader, imaging infrared, pulsar positioning system, and inertial guidance, as well as a datalink to the launching aircraft, making it one of the most accurate missiles ever developed. It also had a built in Mk35 plasma based supercavitation system that allowed it to reach velocities of up to Mach 8, though it could not maneuver while the supercavitation system was active, and as such, the system was mostly used during the cruise phase of its flight, or on terminal approach against a surface target. The system was usually also used moments before impacts to weaken the shield and increase the chance that the missile would be able to penetrate the shield and destroy the target. The warhead was an adaptable compressed magnetic flux generator magneto-hydrodynamic shaped charge warhead, which could be adapted to form one projectile against targets like tanks, all the way to five projectiles against aircraft, or even simple fragments against smaller vehicles and infantry. It massed 500kg, and 16 could be carried in each weapons bay.
==Quotes==
People always ask me what that armor is made of. I always tell 'em, I got no idea, and it's classified, but those plasma bolts don't make nearly as big a hole as they used to. - UNSC Pilot
Those Sniper missiles are a godsend. With the IRSTS, I can find those Seraphs at 300, 400 kilometers, fire off a bunch of Snipers, and watch those Seraphs bite the dust, without ever exposing myself to enemy fire. - UNSC Pilot
You know what a Xiphos is? It's a sword used by the original Spartans. Let me tell you, the modern version lives up to the name in every way. - UNSC Pilot
We were pinned down, the whole company, by this one Scarab with a bunch of Wraiths on support, when out of nowhere, missiles started raining down, blowing off the Scarab's legs, destroying its weapons, gutting the Wraiths, they even tagged a pair of Ghosts with one missile. We found out later that a pair of Scimitars had done that from 500 kilometers away. The bastards hadn't even left their patrol circuit. - UNSC Infantryman