KSM1 Jabber

The KSM1 Jabber (officially SM3 Jabber MBT within the Sironan Militia and M471 Light Tank across the UNSC) is a main battle tank primarily utilized by the Sironan Militia, though it has also seen limited service in the UNSC Marine Corps and UNSC Army, supplementing their . A handful have also fallen into the hands of various cells, though to an even lesser extent than its presence in UNSC service. Smaller and more weakly armored against conventional, human threats than the M808, the KSM1 line nevertheless offers theoretically higher levels of protection against the plasma used by the Covenant, being specifically designed by Kovac and Sons Motor Company to counter the perceived threats presented by the alien invaders while remaining singiciantly cheaper on a per-unit basis than its counterpart.
To achieve these lower costs, the companies involved in the vehicle’s developmemnts were all smaller, local Sironan corporations, rather than the industry giants (such as or ) associated with most UNSC vehicles. This did, however, limit the vehicle’s viability outside of the expanding Sironan Militia and its local supply lines, as logistics was complicated for the UNSC by the divergence from typical partners and lack of cross-compatability with other platforms.
Additionally, the tank and its gun are both smaller and lighter than the Scorpion and its respectively, allowing the similar engine power to provide a significantly more mobile vehicle without dramatically increasing costs. While the terminal effect on the target is lessened due to the smaller, 3-inch (76.2 mm) caliber of the Jabber’s gun (further exacerbated by the common usage of self-sharpening sabot rounds), the usage of Eletrothermal-chemical propellants provided significantly higher and more reliable muzzle velocities and increased penetration, and the unique design of the ammunition and cannon breech enabled faster fire rates. This did, however, lead to trade-offs in the performance of high-explosive rounds and anti-tank missiles fired by the vehicle, both due to the smaller bore size and (for the former) increased velocity requiring thickened walls and reduced filler.
Despite these tradeoffs, the Jabber performed well enough during the Human-Covenant War that the Sirona Militia ordered an upgrade to the tank in the form of the SM3 Seriz 2 Jabber, gradually replacing the older model starting in 2555. The Seriz 2 features slightly thicker armor overall, an additional coaxial 25 mm M68 Gauss Cannon, and a larger turret. UNSC post-war tanks on this upgraded platform instead include the M68B Gauss Cannon (designated the M471B) and, later, the M70 Gauss Cannon (designated the M471C). A handful of select M471B tanks have also seen trial integration of shielding technology, all in the hands of .
== History ==
=== Preceding Efforts ===
The first murmurings that the Sironan Militia could make use of its own main battle tank, rather than relying on coordination with Scorpions, arose in the early 2510s, following the First Battle of Sirona. While the UNSC forces on the ground had managed to quickly defeat the Insurrectionists attacking the Sironan military facilities, the few Insurrecitonist forces that had diverted to instead attack civilian populations faced far less effective resistance from members of the as-of-then unmechanized militia. This was particularly the case for those Insurrectionists who were able to make use of their own captured and makeshift armored vehicles, threats the militia was ill-equipped to counter. While the UNSC was able to handle these lingering forces following the conclusion of the main conflict, many members and leaders of the militia remained frustrated at the loss of life and their lack of effective means to handle armed heavily armed and armored hostile forces in similar future situations where the UNSC would not be able to provide immediate support.
Despite these frustrations and the quick progress in providing the militia with lighter vehicles, lingering distrust among UEG officials of colonial paramilitary groups saw funding for the Sironan MBT program facing limitations and cuts in exchange for an increased deployment of UNSC forces to the planet. As such, many proposals had to be cancelled after initial designs due to concerns over budget, and while two managed to reach trials (the SM1X and SM2X MBTs), the trade-offs required to stay within budget led to subpar performance in one or more aspects of the vehicle. Ultimately, a decision was made to mount the SM2X’s turret and cannon (both derived from Scorpion designs) to the chassis of a SM1 Locust IFV, producing a light tank and interim solution that effectively left the MBT program dead in the water.
Even with the arrival of the Covenant in the mid-2520s, progress remained slow as UEG officials withheld information about the true extent of the threat from colonial governments and populations. However, as the war progressed and more and more worlds were lost, UEG opposition to colonial paramilitary groups—particularly those on Inner Colony worlds—diminished proportional to the similar decline in Insurrectionist activity. With a booming economy driven by the increased demand for medical supplies and the succesful implementation of Colonial Governor Anna Masson's wartime economic reforms, many of Sirona’s smaller companies saw a period of expansion.
=== Development ===
In early-2532, one of these smaller companies, Kovac and Sons Motor Company (KSMC), found itself undergoing rapid explorations into other aspects of the market. Having previously provided the electric motors and fuel cells for the SM1 Locust IFV and its derivatives, company leadership wanted to increase their presence in defense contracting and armored fighting vehicles. Knowing that they could not hope to compete with the larger, inter-colonial firms, the new Combat Vehicles Division saw a way into this market by taking the initiative and approaching the Sironan Militia with a proposal to revive the MBT program with a cheap, quick-to-produce vehicle. With the militia’s own increased funding stemming from the economic boom, KSMC’s willingness and ability to convert automobile facilities into high-end production lines for the tank, and the preliminary concept art showing promise that previous attempts had lacked, the Sironan Militia quickly signed a contract with KSMC to begin further development.
With a budget set within a week of the first pitch, the design process was in full-gear by June of that year. Despite this rapid beginning, progress slowed for a variety of factors: the company’s newcomer status to the industry, the project’s start-from-scratch nature (no longer derived from the Scorpion like previous attempts), and ever-changing information provided to the public about the Covenant’s capabilities leading to significant shifts in design philosophy several times throughout development. Desperate for a MBT after so many delays and failed projects, the Sironan Militia nevertheless provided KSMC ample time and budget to keep working, ultimately stretching the program out for nine years before prototype-ready designs for the vehicle were finally delivered in March 2541. Even after approval of these designs, the development methods to produce titanium diboride armor plates and scale previous KSMC electric motor arrangements up to the much heavier Jabber introduced further delays to production.
The first four prototypes were not delivered to the Sironan Militia until eight months later in November 2541, receiving the militia designation SM3X for testing. By April 2542, the militia returned to KSMC with news of several issues with the tank. The most noteworthy of these issues was that the main cannon—Sironan General Defense’s (SGD’s) 3-inch SGD337 Electrothermal-Chemical Smoothbore Cannon—was too long and proved unbalanced in the Jabber’s turret, leading to significant accuracy issues. Additionally, the suspension and electric motor systems both proved to still be underpowered for an AFV of the Jabber’s weight despite efforts to scale the systems up. The militia also included that additional fuel cells would need to be provided to meet requirements for deployment duration and range.
Returning to the design process, KSMC contacted SGD to commission a new iteration of the SGD337, requesting a reduction in length from 66 calibers to 50 and any tweaks required to the ETC design to still effectively fire the same set of rounds as the original. A budget extension that had been provided following the initial testing afforded the funds necessary to strengthen the suspension and increase the power of the electric motors in-house, and a slight increase in per-unit cost allowances increased the number of fuel cells that could be provided to a single tank. By October 2542, the design for these changes had been finalized and production of fourmore prototypes began, delivered to the Sironan Militia by January of the next year. Receiving the designation SM3X.2 (with the original prototype design retroactively being designated SM3X.1), the vehicles underwent additional testing over the next two months, receiving final approval for production in March 2543 under the final designation SM3 Jabber MBT. With only a few remaining changes proposed for comfort and battlefield identification, production began quickly and units from the original run of 20 vehicles began arriving at militia facilities by July 2543. The original 8 prototype Jabbers were also converted to the finalized standard and delivered by August, alongside the last of the initial production run.
=== Early Service ===
Now with 28 Jabbers at their disposal, the Sironan Militia faced another issue, this one logistical. While the systems to refuel the previous militia AFVs were compatible with the tank, there were significant capacity issues. One base had been upgraded to meet the needs of refueling the larger vehicles, but this base only had space to house seven Jabbers, leaving the remaining 21 without the facilities to operate effectively out of the remaining three militia bases. Expansion of refueling stations thus became a priority in the militia bases outside of Maponos, Bodua, and Esos while the Grannus facility (with the full-capacity stations) became the primary training facility to bring militia tankers up to speed with their new vehicles.
By October, all four bases had been upgraded to be able to refuel their tanks, with training on the vehicles redistributing across all four facilities and all 28 Jabbers, effectively quadrupling the rate of familiarization. By the middle of December, the last of the militia tankers had qualified on the vehicles, culminating in a tank crew competition across the four militia bases by December 20. During this competition, UNICOM had its first exposure to the Jabber. Impressed by the performance of the vehicles that he saw on display, a Marine armored division Colonel (present on the planet to recover from wounds he had sustained during the fighting on the Atlas moons) informed his superiors of what he saw. By February 2544, this information had worked its way up the chain of command and saw a contract between the UNSC Marine Corps, Sironan Militia, and KSMC to produce a second run of Jabbers, this time for the UNSC Marine Corps. With fighting picking back up in the Valence system in May 2544, the final stages of production were rushed to send a shipment of vehicles alongside a redeployment of Marines to the Atlas moons that June. Fulfilling this by sacrificing numbers, KSMC managed to roll a set of twelve Jabbers out of the originally ordered 20 off their production lines in under four months from the initial order.
=== Atlas Moons Campaign (2544-2545) ===
=== Siege of Sirona (2544-2548) ===
==== Opening Days ====
Only a few months after the Jabbers left for the Atlas Moons, those that were left behind in militia control on Sirona saw combat of their own. On July 25, 2544, the Covenant launched an attack on Sirona, plunging the world into what would become a siege that lasted for nearly four years.
=== Rebuilding Sirona ===
=== Seriz 2 Development ===
=== ONI Energy Shielding Trials ===
=== Second Battle of Sirona ===
=== Created Conflict ===
== Role and Usage ==
== Design Specifications ==
=== Armament ===
==== Primary ====
===== SGD377A1 Smoothbore Cannon =====
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The main armament on both the KSM1 and KSM1 Seriz 2 tanks is the 3-inch SGD377A1 Electrothermal-Chemical Smoothbore Cannon firing primarily a tungsten armor-piercing fin-stabilized discarding sabot (APFSDS), canister, or high-explosive dual purpose fin-stabilized (HEDP-FS) round. This cannon was an iteration on a previous anti-tank gun produced by Sironan General Defense, a small, locally founded defense contractor who had previously worked with the Sironan Militia. Due to the small caliber (despite the tank itself also being relatively small) a large number of rounds could be stored, with the KSM1 turret holding 60 and the KSM1 Seriz 2 holding 65. Additional rounds could also be stored in the hull in both models, but this was not often done, as these rounds did not have the same isolated storage as the turret rounds did, and did not connect to the autoloader system. Finally, the tank could also fire anti-tank guided missiles, with up to five being stored behind the tank commander in the turret bustle, able to be manually loaded when needed.
While the original plan was to use the original SGD337—a 16 ft 6 in (66 calibers) anti-tank gun developed by Sironan General Defense specifically for anti-Covenant use during the early days of the Human-Covenant War—issues with turret balance saw the development of the SGD377A1, cut down to 12 ft 6 in (50 calibers). While testing showed that the reduced barrel length did modestly affect muzzle velocity, the problems with mounting and production capacity proved to be more detrimental than the loss in potential penetration power, with the shorter gun still being able to penetrate analogues to Covenant armor at an acceptable engagement range. The final production cannon had a gun depression of 9 degrees and a gun elevation of 20 degrees when mounted in the KSM1 turret and a gun depression of 10 degrees and gun elevation of up to 22 degrees when mounted in the KSM1 Seriz 2 turret. Additionally, it possessed an automatic stabilization system that could keep the gun level while driving at maximum velocity over rough terrain with enough precision to reliably hit targets out to its effective range in over 95 percent of cases during testing. Often, better results were seen during actual combat due to favorable differences in engagement ranges and conditions.
The core of the APFSDS round fired by the SGD377A1 comprised of a primarily tungsten alloy 1.25x15.5 inch penetrator. While tungsten on its own was considered largely substandard as a tank round by the designers of the vehicle, recent advancements in the years before the Human-Covenant War had led to the discovery of an alloy which possessed both the self-sharpening and incendiary effects of depleted uranium alloy penetrators without the innate toxicity, leading to increased penetration and the chance for potential additional internal damages once the round pierced the target. Combined with the approximately 2,450 meters per second muzzle velocity (just under the hypervelocity threshold) produced by the electrothermal-chemical propellant utilized for the APFSDS rounds for this cannon, the SGD377A1 firing APFSDS rounds could reliably penetrate analogues for Covenant armor out to 4,000 meters, though it has been anecdotally seen success out beyond this range when targeting more lightly armored vehicles. While issues were present with post-penetration damage compared to the larger round offered by the Scorpion or Grizzly tanks in UNSC service, the single- or dual-crewed configuration of most Covenant armor paired with the accuracy and rapid fire rate of the cannon effectively mitigated any perceived issues in field use.
The second shell option for the SGD377A1 was a canister round. Unlike the canister rounds on the Scorpion, which fired a cylinder containing the eventual shot to be released upon impact, the canister round for the SGD377A1 worked much more like an oversized shotgun, immediately spraying roughly 80 small metal spheres out from the gun's barrel. This was particularly effective against nearby infantry units, though the relatively tight grouping of the shots allowed it to remain reliable out to about 250 meters. Once again, however, the canister round is limited in effectiveness by the smaller caliber of the SGD377A1, leaving the gun unable to fire as many projectiles as the cannon on a UNSC MBT could.
For its HE option, the SGD377A1 was provided with a HEDP-FS round, though this proved less reliable against heavy Covenant armor than the APFSDS. Additionally, muzzle velocity and thus range was reduced compared to the kinetic round, as the walls were thinned and propellant charge reduced to maximize the already small volume available for explosive filler without risking premature detonation. While the nature of the round meant it did not lose penetration over range like a pure kinetic penetrator would, these two limitations made it rare that a Jabber facing heavy armor would choose it if the APFSDS was available regardless of range. Beyond anti-armor uses, the existence of the canister shot overshadowed the HEDP-FS in close-range anti-infantry work. Ultimately, two situations provided the round a chance to truly shine: use against fortifications and light armor, and long-range anti-infantry work. In the former, the fragmentation effect of the round often dealt more damage than the APFSDS option without risking overpenetration, more easily disabling the threat in a single shot; in the latter, the round remained effective well beyond where canister shot would begin to fall-off and could more easily deal with clustered infantry than the precision nature of the APFSDS or even the vehicle's various machine guns.
All three shell options for the Jabber were cased telescoped rounds 5 inches in diameter and 18 inches long, with the opening for the projectile being 3 inches to match the bore.
One of the primary features of the SGD377A1 was its use of an automatic loading system via a swinging breech, replacing the need for a fourth crewman in the vehicle. The rotational alignment of the swinging breech and the cannon's trunion allowed it to be loaded regardless of barrel elevation. While the tank was still capable of being manually loaded in the event of an autoloader failure—with the breach able to be locked in alignment with the barrel and the rear opened for access—this was considered an unlikely enough situation that the benefits of only having a three-man crew outweighed the possibility that the tank commander would have to take over loading duties should it occur. To facilitate this emergency manual loading, access to the bustle ammunition tray was available through a manually operated door behind the tank commander's seat. 
The autoloader itself fed from the bustle, along the right side of the turret, and through a door to end up below the gun where it was aligned with the swinging breech and inserted. The door between the ammunition compartment and the rest of the tank was automatically operated, remaining closed when a round was not being fed. Within the ammunition compartment, 25 of the turret stowed rounds were available as "ready rounds" on the autoloader's cassette along the righthand side of the turret while the remaining rounds were located further leftward and would have to be fed onto the autoloader between combat encounters by the commander through a second access hatch. This system allowed more rounds total to be stored in the turret than would otherwise be available if all of them were connected to the autoloader. Additionally, the gunner had the ability to rotate the cassette to select a particular round as part of the Jabber's fire control system.
The three armored doors in the turret allowed for the ammunition to be separated from the crew-compartment, reducing the risk of crew loss in the case of a direct hit on ammunition when combined with emergency blow-out panels on the top of the turret's ammunition compartment. Furthermore, the turret basket itself was armored and sealed off from the driver and gunner seats in the hull of the vehicle. The safety of these features was what allowed the ability to operate the Jabber with a manned turret as a fallback in case of an autoloader failure without compromising crew survivability to an unacceptable degree.
The autoloader system had a cycle of 1.75 seconds for reload. Here, the spent casing was ejected through the top of the breech by the next round pushing it out, permitted without damaging the round by the cased telescoped nature of the rounds. While this was occurring, the gunner could still aim as the autoloader would be able to compensate for changes in elevation over the short period loading operations required. With calculations taking place during the aiming process, there was minimal if any delay between the gun finishing loading and the next shot being ready to fire, provided a new shot could be acquired rapidly enough. Field operations often saw the ability of the gunner to select and aim at a new target to be the limiting aspect on fire rate, rather than a new round not yet being ready.
===== M68(B) Gauss Cannon =====
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The post-war SM3 Seriz 2 Jabber MBT and early M471B Main Battle Tank models also saw a second primary armament mounted coaxially to the right of the SGD377A1 cannon. This took the form of surplus M68 Gauss Cannons for the SM3 Seriz 2 and M68B Gauss Cannons for the M471B. The surplus weapons were provided by the UNSC to the Sironan Militia, who were looking into replacements for the older weapon in their own vehicles, had already moved on to the M68B, and felt the Jabber needed to supplement the efficacy of its main cannon. While only firing one type of ammunition when used by the Sironan Militia, the M68 became the primary anti-fortification weapon of the post-war Jabber due to the hypervelocity nature of the projectile it fired, with HEDP and HESH rounds not being provided to Seriz 2 Jabbers as a result. This further motivated the addition of the M68B to the M471B, as the UNSC operators of the tank would only need to contract for two types of proprietary round, rather than the four they needed on the original run of the Jabber.
While this weapon did not require any additional development in and of itself, its inclusion in the tank did directly lead to changes for the Seriz 2 compared to the original Jabber, primarily in a larger turret (in all three dimensions) and the incorporation of an additional ammunition compartment below the gunner to accommodate the rounds and loading mechanism for the gauss cannon, the inert nature of the rounds making this storage situation safe despite the lack of isolation. This compartment could store up to 80 rounds for the M68 on a chain feed system, allowing it to automatically reload the weapon. Additionally, the weapon was mounted on its side, with rounds loading into the bottom and the linkages ejecting out the top of the tank.
Firing 25x130mm high-density projectiles at up to approximately 13,700 meters per second, the M68 Gauss Cannon aimed to take advantage of hypervelocity impacts to damage the targets it hit. Rather than directly penetrating what it impacts, the extreme energies of the collision result in the projectile and its target behaving more like fluids than metals, with both vaporizing upon collision, often in large segments when it comes to the impacted target. These impacts can also often lead to plasma discharges as the air around the area is superheated, often making them easy to mistake as explosions when combined with the similar results they show. While typically utilized in an anti-vehicle role when mounted on Warthogs by the UNSC, this behavior actually led to it being primarily utilized for anti-fortification roles, as the SGD377A1 cannon provided more effective penetration and internal damage to vehicles with its APFSDS rounds while the M68 rounds could provide larger impact craters to leave a bigger hole in static structures.
When mounted on the new iteration, the M68, M68B, and M70 Gauss Cannons—by nature of being coaxial with the SGD377A1 cannon—had the same elevation and depression values. However, they fired at a faster rate (approximately one-second reload time) and did not recoil within the turret, transferring the force into the vehicle itself much like in its other applications.
===== M70 Gauss Cannon =====
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==== Secondary ====
The KSM1 has two machine guns:
#A 11.5x90mm SSA (.453 caliber) SSA338 Heavy Machine Gun on a remote weapons station located on the left side of the top of the turret, just in front of the commander's hatch, controlled by the tank commander. This allows the weapon to be aimed and fired from inside the tank, providing increased protection for the tank commander when in a combat situation requiring its utilization. Developed by Sironan Small Arms in the later years of the Insurrection—keeping consistent with the Sironan Militia's dedication to the company—the SSA338 was similar to the M247H machine gun used by the UNSC, albeit smaller and cheaper with a proprietary round. While the 223 also had a faster rate of fire (750 RPM cyclic) than its UNSC counterpart, this came alongside a shorter effective range. However, testing by Kovac and Sons Motor Company and the Sironan Militia showed the weapon to be sufficiently effective within the expected infantry engagement ranges of the tank while being provided at a significantly cheaper cost. 750 rounds of ready ammunition were available for this weapon.
#A 6.9x59mm SSA (.272 caliber) SSA333 General Purpose Machine Gun mounted coaxially slightly above and to the right of the main gun. Much like its bigger sister, the SSA338, the SSA333 was comparable to the standard UNSC M247 machine gun, albeit smaller, cheaper, using a proprietary round, and with a increased rate of fire (800 RPM cyclic). Unlike the SSA338, however, the 107's higher pressure cartridge and lighter bullet saw an increase in effective range for the weapon. Altogether, the SSA333's specifications were also found to be within acceptable limits during testing. 4,500 rounds of ready ammunition were available for this weapon, stored on a belt above the cannon's autoloader along the right side of the sealed turret compartment.
While the SSA338 could be replaced by standard UNSC heavy machine guns on the M471(B/C), and often were to reduce logistical impact, doing the same for the SSA333 would have required not-insignificant alterations to the coaxial mount and internal ammo stowage.
Following the war, the Seriz 2 saw an increase in ammo capacity afforded by the larger turret. In this larger variant, the SSA338 was able to be supplied with 900 rounds and the 107 with 5,000. Additionally, the ready ammunition capacity in both versions of the tank could be bolstered with resupply boxes elsewhere in the hull, allowing reloading of the ready ammunition compartments.
==== Aiming ====
All Jabbers are equipped with a ballistic fire-control computer that uses both system and user-supplied data from a variety of sources to compute, display, and incorporate lead angle, range to the target, and selected ammunition type into one single firing solution for the gunner, allowing the main gun to be fired accurately. Additionally, the gunner has the option to use the computer to automatically select any of the shell types available in the autoloader cassette to prepare as the next round. Laser rangefinders, crosswind sensors, tracking rate tachometers, and static cant sensors, as well as situational data about shell type-dependent flight characteristics, tank-dependent bore alignment, and a variety of temperature-based effects are all incorporated into the computer's calculations to determine these three factors. This firing solution is updated at over one-hundred times per second and incorporated into the reticle on the gunner's sight in all modes, allowing the gunner to reliably hit the target by simply keeping the displayed reticle on it, vastly simplifying his or her job.
The gunner's sight itself can view across a wide range of the electromagnetic spectrum, though the most commonly used settings are thermal and visual. While it is called the "manual sight" in its name, this only refers to the fact that the gunner has the ability to use it manually, boresighted to the main gun and coaxially weapons, should the targeting system fail, not that he is required to aim manually using it. In fact, the sight is the primary method for the gunner to aim the weapon even when using the fire-control computer and is the device onto which the targeting reticle is projected. In addition to the gunner's sight, the tank commander can also get an external view of the tank using the commander's Independent Multiwavelength Viewer (CIMV). This device, with the capabilities to cover the same wide range of the electromagnetic spectrum as the gunner's sight, allows the commander to locate targets and pass them on for the gunner to engage while the commander scans for new targets. The CIMV also links with the commander's Weapon Station to aim and control the remotely operated SSA338 HMG should the need arise.
In addition to the two primary target-acquisition systems for the commander and gunner to utilize, both also have access to a passive sensor system to detect strong external emission signals that might indicate an enemy out to a maximum range of two kilometers, and the tank commander can activate an active air detection radar system to detect incoming aircraft. On top of this, each of the three crew members had screens available to access any of the visualization systems on the Jabber regardless of direct proximity, allowing access to 360 degree, multi-wavelength awareness around the tank, bolstered by several integration systems within the vehicle's computers to better present the data.
Following the war, licenses for both of these systems were provided to off-world companies in contract with the UNSC as part of an effort to ease the logistical burden the Jabber showed itself to be on the Atlas Moons. The effort proved successful, with optics replacements becoming no more difficult to acquire for M471 and M471B Jabbers than Scorpions by as early as 2555.
=== Crew Layout ===
=== Armor ===
Primarily designed to fight the Covenant and their plasma weapons, the tank varied from typical defense design in one important manner. While it remained a composite armor system, consisting of layers of Titanium A alloy, open space, plastics, and hardened ceramic blocks, the specific ceramic used was changed. While ceramics generally have the capability to resist high heats, the 3,000°C temperatures reported for some heavy Covenant plasma weapons required something with a higher melting point than the typical silicon carbide. As a result, the decision was made to instead utilize a form of titanium diboride, sintered into coherent plates. While the material was slightly denser and more expensive, the difference that would result in total weight and cost were negligible due to the small size of the Jabber. In turn, the material offered comparable hardness (important for shattering kinetic impactors) and a significantly higher melting point than the alternative, resistant to heat up to over 100°C beyond the highest recorded Covenant plasma temperature. While the armor would still have to deal with the concussive force from direct impacts or near misses from Covenant weaponry, this aspect of the attack was mitigated by the remaining layers of the armor, much like a HEAT shell's blast would be dissipated before making it to the interior of the crew compartment.
Another difference in the Jabber's design was the layout of the armor. While it was common to see tanks mount composite armor only on the front of the vehicle's hull and turret, the decision was made to also cover the entire top hull of the Jabber. This was a design choice intended to bolster two factors of the KSM1's intended role: the ability to work within an urban environment and the ability to directly face Covenant forces. For the former factor, the increased armor on the top of the tank served as additional protection against attacks from above. For the latter case, the decision was made specifically to counter indirect fire methods that the Covenant often deployed, specifically from vehicles such as the Wraith or Revenant. In addition, the sides of the turret and the spaced armor skirting placed along the exterior of the Jabber's tracks were both constructed from a composite, though these components made use of the lighter silicon carbide construction to cut down on weight in less vulnerable positions. The remaining faces of the tank's armor consisted of simple Titanium A armor plates, serving only to protect against smaller arms fire, with the decision made to cut down on weight and increase the vehicle's mobility.
In addition to changing which sections of the tank were most heavily armored, the geometry of the layout also differed from conventional doctrine. While sloped armor was known to be effective against kinetic, shaped-charge, and other linear means of penetration, these were considered secondary threats to the Jabber. With armor that could stand up against melting against the heat of even the most extreme covenant plasma weapons, the only direct threat to the vehicle was via explosive mechanisms. Designed to defend against the Covenant rather than human insurrectionists, the form that explosives the vehicle would take most often would be spherical, omni-direction, contact-detonated charges as seen in vehicles like the Wraith and Revenant, or from the various fuel rod cannons. Given that such rounds would have equivalent penetrative power regardless of the angle at which they approached the armor (a flat plane that touches a sphere at only one point will always be tangent to that sphere), sloped armor was largely forgone in the vehicle, allowing for more usable space in the tank's interior without adding additional weight or increasing the overall volume. All-in-all, these decisions afforded the Jabber considerably more interior space than comparably-sized tanks without forgoing protection against Covenant small arms, the main enemy they were intended to combat.
Upon receiving additional funding in the post-war era, the Sironan Militia up-armored the KSM1 Seriz 2's larger turret by increasing the thickness of the turret's side armor and implementing titanium diboride composite armor on the rear. This decision was made following an investigation into the Jabbers that had been knocked out during the Human-Covenant War which had revealed that a large number of Jabbers had been disabled due to Covenant indirect-fire plasma weaponry impacting the rear of the tank, behind the turret. Upon impact, the simple Titanium A plating proved insufficient to disperse the force from the plasma before it could ignite the ammo stored inside, rendering the vehicle inoperable. While the doctrine of the militia to make use of the Jabber's mobility and have it advance under the arch of the incoming plasma and close the gap caused this situation to occur more often, the fact that this doctrine proved successful for Jabbers that avoided such impacts led to the decision to armor the rear of the turret against the plasma, rather than change strategies to something that avoided the hit in the first place.
Also making use of the increased post-war funding, the Sironan Militia began upgrading existing KSM1 and new KSM1 Seriz 2 tanks with slat armor over the rear of the tank's hull. These served to disperse the containment fields of plasma weaponry and decrease their effectiveness before reaching the actual hull of the vehicle without needing to add a significant amount of weight to the design. While this proved to only truly be effective against the fuel rod cannons of the post-war Covenant remnants, the low cost and impact on total weight justified the minimal increase in effectiveness.
Other changes saw the shaping of the armor plates the be consistent with UNSC manufacturing capabilities, allowing the vehicle to be re-armored more easily when in service by UNICOM operators. This was also the case for the slat armor, with both systems implemented to conform with the new requirements on the vehicle stemming from the lessons learned about the logistical shortcomings seen on the Atlas Moons.
==== Energy Shielding ====
A select few M471B MBTs were selected by ONI for an energy shielding trial in late-2556. The Jabber was chosen as it was cheaper and not in as high demand as a Scorpion at the time, affording ONI more flexibility in the experimentation. In total, six Jabbers were requisitioned, of which three were successfully equipped with energy shielding, with the others being utilized as a control group. Of the three Jabbers fitted with energy shields, different modifications were made to afford the space for the system. For one, several fuel cells were removed. For another, an extra compartment was added on to the back of the Jabber turret. For the last, the fresh-water tank beneath the crew-compartment was removed and the water produced by the spent fuel cells was instead allowed to leave the vehicle as exhaust.
By the conclusion of the trial, it was determined that the possibility for energy shielding on MBTs (both the Jabber and Scorpion) would be too cost prohibitive for the negligible benefits and considerable trade-offs present in implementing the system. Instead, ONI changed their tune and focused on experimental weapon and upgraded conventional armor systems for their variant of the upcoming .
=== Countermeasures ===
==== Active Protection System ====
==== Camouflage ====
The KSM1 and KSM1 Seriz 2 were both coated with a monotone (pale tan) primer layer directly on top of the armor plating. On top of this, several different patterns could be applied depending on the expected situation. These consisted of woodland, desert, and urban varieties. Of these, urban was the most commonly applied due to the nature of the expected environments in which the Jabber would be fighting.
The M471, 471B, and 471C MBT versions of the Jabber were shipped with just the monotone primer coat onto which standard UNSC patterns could be applied.
==== Concealment ====
The turret is fitted with a pair of eight-barreled SGD291A5 smoke grenade launchers, produced by Sironan General Defense. One launcher sat on either side of the main gun. These grenades airburst after deployment, creating a thick smoke that blocks visual, infrared, and millimeter wave imaging and targeting. This smoke consists of a mixture of standard, optically-obscurant particles and more advanced carbon fiber obscurant that absorb across the infrared and millimeter bands. The inclusion of these later particles can block some radar applications, as well as most thermal imaging and infrared laser designation.
These smoke launchers are able to fit and launch several varieties of UNSC-standard smoke grenades, one of the few systems that were already compatible on the original version of the Jabber.
==== Damage Control ====
Similarly to the fuel cell deck, the crew compartment of the Jabber has an inert gas firefighting system. While the fuel cell deck is continuously flooded by inert gas, the occupied nature of the crew compartment means that the system instead keeps the gas enclosed in storage to be released automatically upon the detection of a significant enough fire. The amount of gas is carefully formulated to extinguish all but the largest fires while also remaining in low enough concentrations to avoid suffocation or barotrauma for the tank crew. The compartment also contains small, hand-held fire extinguishers for situations that have not set off the automated system or in the case of an automated system failure.
As the tank featured an autoloader, the ammunition could be stored in a separate compartment from the crew, blocked off by sealed armor plating or the autoloader itself except when a round was being loaded. The manual loading door was required to be sealed before the main gun could fire, and was kept as such unless there was a failure in the autoloader, closing automatically once a round was retrieved in the case of manual loading. The addition of emergency blow-out panels on the top of the tank's ammunition compartment compounded with these safety features to make ammunition cook-off or explosions very safe for the crew.
==== Magnetic Field Generators ====
For the KSM1 Seriz 2, tests were conducted into magnetic field generators to actively disrupt these containment fields from a larger distance in a sphere around the entire tank, but these systems did not prove cost-effective and were only implemented on a handful of tanks before the program was shut down. However, the tanks on which the system was implemented did not see any significant combat, particularly not against forces which made use of plasma weaponry. This was largely a result of the lack of such systems on any M471B or C variants. As such, there was minimal actual field testing to judge the success of the program.
=== Mobility ===
==== Engine ====
The Jabber comes equipped with the proprietary Kovac and Sons Morvarc'h Hydrogen Fuel Cell/Electric Motor System. This system consists of an array of hydrogen fuel cells found in an isolated compartment to the rear of the tank providing electricity to drive a pair of motors at a combined maximum 2,012 shaft horsepower (1,500 kW) in the constant power range of the motors above 3,000 RPM and a combined maximum torque of 3,522 foot-pounds (4,775 Nm) in the constant torque range below 3,000 RPM. Due to the nature of electric motors, these are connected to the drive wheels at the back of the vehicle's track through a single-speed 10:1 step-down transmission, with reverse managed by electronically triggering the electronic motors to spin backward, driving the tank up to an electronically limited maximum speed of 20 mph (32 km/h). This system is capable of obtaining an electronically limited maximum speed of 50 mph (80 km/h) on paved surfaces falling down to 35 mph (56 km/h) cross-country. While theoretically higher speeds are possible with the electronic limiting system disabled, increased risks of crew injuries, higher maintenance requirements, and the lack of practical use of higher speeds in previous combat situations have seen the limiter remain enabled on the vast majority of KSM1 tanks.
While there were originally concerns about the power demands of the tank, with the electronic systems of the vehicle requiring electricity even while the motors aren't running and the motors themselves demanding extensive electrical draws from the fuel cells when they are, the large configuration of fuel cells taking up the rear compartment of the tank covers for this, allowing for a maximum range of approximately 450 miles before requiring refueling, or over three days of continuous idle running of the tank. Fuel cells were primarily chosen for this reason, presenting a significantly higher energy density than contemporary battery systems, saving space (and thus weight, due to the extra armoring required to enclose a larger volume) compared to a battery array that could provide comparable performance. Additionally, compared to ICE systems, the lack of byproducts except for pure water (collected in a tank beneath the vehicle's fuel cell compartment) allows the tank to operate without an exhaust system. This allows infantry to operate close to the tank without potential for injury due to high-temperature or high-velocity gas emissions. Furthermore, the electric motors run significantly quieter than traditionally fueled engines while also requiring less maintenance as a whole due to the decreased complexity of the design, lacking automatic transmission fluid and motor oil as well as having generally fewer components as a result.
The fuel cell compartment of the KSM1 tank is flooded with an inert gas to counteract the inherent flammability of the fuel cell technology should it get struck by enemy fire. Additionally, this serves to remove the chance of any incident fires sparking as a result of the high temperatures (150 to 200 degrees F) that the fuel cell array operates at. This excess heat is radiated mostly through the rear bottom of the tank, allowing the temperature of the resultant heated air to decrease significantly before reaching a point where it could potentially cause injury to accompanying infantry or the tank crew itself. While the fuel cell array itself has a continuous operation lifetime over up to 50,000 hours, the mileage lifespan of the electric motors is more commonly the limiting factor determining when a Jabber's power system requires maintenance, repair, or replacement, typically only offering a lifespan of just over 30,000 miles.
==== Refueling ====
Refueling the Jabber can be done through two methods. The primary method of refueling is to make use of a dedicated refueling facility to pump oxygen and hydrogen directly into the vehicle through a pair of ports to the rear left of the tank. This is the secondary reason the fuel-cell system was chosen over a battery, as the Jabber was built to be able to make use of any pre-existing UNSC facility for refueling hydrogen ICE vehicles. While batteries are ultimately more energy efficient, the pre-existing architecture allowed the Sironan Militia to save a large amount of credits and logistical effort for minimal trade-off, especially given the previously mentioned energy density considerations.
However, if this is unavailable, the Jabber can connect to a wide variety of power sources to directly convert stored water to usable fuel through electrolysis carried out by an internal system connected to the water tank. The port for this connection is located to the rear right of the tank. A portable solar panel system is carried on the majority of Jabbers, capable of generating ten miles worth of fuel an hour on sunny days, designed to provide a method to temporarily refuel a Jabber if it was driven to a standstill without static refueling or power generation stations within range, though this situation proved rare due to the warning issued by the KSM1's fuel management system as the fuel cells came closer and closer to empty.
==== Suspension ====
The Jabber runs on 6, 750mm road wheels per side, each mounted on an independent hydropneumatic suspension unit. While these suspension units are active, with hydraulic actuation, they are often independently set prior to installation based on expected terrain and load to reduce the strain on the tank's hydraulic pump via a reduction in the actuation required to account for uneven roads. However, the benefits of doing so are relatively minor due to two factors. First, the front road wheels of the Jabber are lifted off the ground during turns below about 10 miles per hour (above which the extra stability is judged to be a more important factor) in order to reduce track contact with the ground and allow for quicker turning and reduce maintenance requirements on the tracks. Second, the actuation can be manually controlled by the driver to afford the tank extra gun depression or elevation by making the vehicle "kneel" (raise the rear and lower the front) or "crouch" (raise the front and lower the rear) respectively. As such, the vehicles very often saw heavy use beyond adapting to the terrain from their initially set position.
The drive sprocket resides in the rear of the Jabber, with the front wheel serving simply as a guide wheel and to provide tension. This was mostly due to the location of the fuel cells and electric motors in the rear of the vehicle, but also served a purpose as the tank saw use and the tracks lost tension and lengthened over time. It was considered better by KSMC to allow the resulting slack to be pulled by the rear wheel and thus reside on the top portion of the track, draping along the return rollers, than to force the track to be pulled from the front and thus have the slack reside along the ground. This also resulted in less of the track being under full tension and thus reduced wear. While these tracks were originally independent developments by KSMC, the Seriz 2 saw them replaced by the track links used on the front booms of the , albeit in longer chains. In association with using drive sprockets and road wheels similarly available, the changes allowed the new version of the tank to better take advantage of existing supply lines.
The hydropneumatic units themselves consist of a suspension sphere—connected to the tank's hydraulic fluid reservoir and pump via a suspension cylinder—which contains a volume of nitrogen (due to its lack of corrosive properties) trapped and separated from the hydraulic fluid via a rubber membrane. While the hydraulic fluid itself is incompressible mineral oil (to avoid water bubbles), the hydrogen can compress and expand with changes in pressure and thus acts as the spring for the system. Crucially, this spring mechanism behaves with non-linear force-deflection characteristics, allowing the suspension systems to easily avoid eigenfrequencies that may amplify or continue variations in the terrain into the tank itself as a linear spring system would be at risk of. This removes the need for additional dampening systems and is a critical part of the unit's relative lack of complexity and ease of maintenance or replacement. The leveling is controlled via automatically adjusting the amount of hydraulic fluid in the sphere, with the "kneeling" and "crouching" positions—as well as the lift of the front wheels during turning—being special implementations of this process.
==== Tank Desant ====
Although the KSM1 is not designed to easily carry riders in the same way the Scorpion was, with the upper rear of the tank's hull being not only small but also often uncomfortably hot due to the operating temperatures of the hydrogen fuel cell system (even accounting for the directional cooling system), provisions can be made to allow the Jabber to carry a small number of infantrymen in tank desant. This is achieved by locking the turret forward and utilizing ropes and equipment straps to provide handholds on the flat front upper hull of the tank. However, Sironan Militia doctrine does not recommend this strategy due to the exposed position it places the infantry in and the limitations it puts on the ability of the tank to quickly fire upon spotted enemies. Additionally, if the mounted individuals are not aware of where they are positioning themselves, they can often block the driver's view. As a result, this tactic was not often seen used by operators of the KSM1 tank.
==== Strategic Mobility ====
Contrary to the tactical mobility inherent to the tank itself and how it navigates the battlefield, strategic mobility is the ability of multiple vehicles to arrive in a timely, cost-effective, and synchronized fashion. For the Sironan Militia, this was not a major concern due to the nature of the force, with a focus more on quick but local defensive reactions. As such, the inherent mobility of the KSM1 proved effective enough to get the tanks into positions to respond to advancing threats within the standards expected of militia readiness. For the UNSC, however, the few M471, 471B, and 471C tanks that they operated received slight modifications to address apparent deficiencies in strategic mobility of the vehicle compared to the Scorpion.
Particularly—while the vehicle was smaller and lighter than the Scorpion—considerations had not been made for UNSC air-lift capabilities, instead carried by atmospheric, Sironan-based lifters. As such, production KSM1 tanks, in both the original and Seriz 2 configurations, lacked attachment points to allow UNSC dropships, such as the Pelican, to carry the vehicle beneath their tails. Additionally, the Jabber lacked compatible points to which clamps could attach to the floors of UNSC frigate vehicle bays for atmospheric deployments. Both of these features were easily added, however, to UNSC models and few other changes proved necessary, with the size and weight remaining within the confines of what the UNSC was capable of transporting effectively.
However, a significant portion of original KSM1 tanks on Sirona—particularly those on the capital island, both militia and UNSC operated—saw the addition of attachment points for an amphibious conversion system. This was a temporary air cushion and propeller/rudder system that could be attached to the outside of the tank to allow it to deploy from Wet Fleet landing craft without submitting the landing craft themselves to shore-based fire. This system was later discontinued after the Siege of Sirona proved that such amphibious-capable craft proved less effective than airlift transport of standard Jabbers over the impeding body of water. Another factor in this decision was that Sironan Militia Jabbers saw minimal movement between theaters during the siege, typically remaining to defend their original position as per the doctrine of the militia as a local defensive supplement to the more mobile UNSC.
== List of Appearances ==