"The Eighty-Six's closest companion, as well as their final resting place." ― Volume 1 Chapter 2
The M1A4 Juggernaut (ジャガーノート, Jagа̄nо̄to?) is the sole Feldreß of the Republic of San Magnolia, manufactured by Republic Military Industries. While developed as an answer to the hordes of advanced drones of the Giadian Empire's Legion, the Juggernaut is markedly inferior to the various types of Legion in firepower, protection, and mobility. Its classification as an unmanned weapon is an ostensible one, as the machines are piloted by the Eighty-Six, who are deemed non-humans under the Republic's discriminatory policies.
A Juggernaut in current English usage is a literal or metaphorical force regarded as merciless, destructive, and unstoppable. The word originates from the Hindu deity Jagannath. Its designation of M1A4 stands for Model 1 Alteration 4.
The silhouette of the Juggernaut resembled that of a prowling spider, but the two grappling arms and its brandished main battery are reminiscent of a scorpion's tail and pincers. It is a machine with four long, jointed legs with whitish-brown aluminum-alloy armor. The legs are fitted with oscillation sensors to detect approaching ground enemies and its maneuverability is slightly superior to that of a treadmill tank.
A Juggernaut's cockpit is similar to a jet fighter's, it has a clamshell cockpit and the inside is filled with a multitude of switches, LCD screens, and twin control sticks to the left and right. The biggest difference was that instead of a bulletproof glass windshield, the Juggernaut's cockpit was enclosed by an armored canopy, so the pilot could not see outside the unit. To compensate for that, the cockpit was equipped with three screens and a holo-window that provided all data of the battlefield. However, the resolution for these displays is extremely low, which leads to low crew visbility and awareness. Due to the crampedness and darkness of the cockpit, Processors often nickname it as the 'Coffin'.
For its main armament, the Juggernaut is equipped with a 57mm smoothbore gun that can fire APFSDS and HESH rounds. The APFSDS - Armour Piercing Fin-Stabilized Discarding Sabot projectiles are used against heavy armoured Legions such as the Löwe. The HESH - High Explosive Squash Head rounds are used against light armoured Legions such as the Ameise, and against fortifications like concrete bunkers and gates. For its secondary armarment, the Juggernaut is equipped with two 12.7mm heavy machine guns. High-frequency blades are also able to be attached in place of the machine guns but are rarely used because of their extremely short attack range. On top of it, two sets of wire anchors are also fitted to a unit for various uses on the battlefield.
As it is classified as a drone, it is minimally armored and not equipped with any sort of life-preserving equipment such as airbags .
At the start of the war with the Giadian Empire, the technological inferiority of the Republic of San Magnolia was made clear. Within half a month, the Republic Army was decimated and its remnants forced to using delaying tactics to prolong the war. It was necessary to produce a new weapon that could fight the Legion's overwhelming numbers.
By the end of the first year of war, Republic Military Industries completed their development of a new vehicle, which was based on technology recovered from Legion wreckage, and quickly started production. However, the new M1A4 Juggernaut was a rushed design, resulting in it being inferior in many aspects to the Legion. Lack of development time forced the Juggernaut to only have a four-legged movement program, unlike the more complicated six-leg systems of the Ameise and Grauwolf and the eight-leg system of the Löwe. In turn, this forced it to be lightly armored and armed to meet the weight constraints of its quadrupedal movement system. The 57mm gun, while sufficient to destroy the Ameise and Grauwolf, cannot penetrate the frontal armor of the Löwe, making frontal attacks on this type of Legion near suicidal. In contrast, all the combat types of Legion can easily destroy the Juggernaut's light armor, which is not even capable of standing up to the 12.7mm machine guns of the Ameise. The quadrupedal design also meant that the Juggernaut has a much higher ground pressure than the Legion units due to its weight being distributed to only four legs. This forces the Juggernaut to avoid soft, marshy terrain or risk getting stuck. Despite these flaws, the lack of a better machine made the Juggernaut the primary weapon of the Republic.
Unknown to the Republic citizens, who knew of the Juggernaut as an autonomous drone, the Juggernaut has to be piloted by Eighty-Six since the Republic is not advanced enough to develop a combat AI equal to that of the Legion. Since the Eighty-Six are considered non-humans, the Republic is able to fabricate the lie that the Juggernaut is not manned by humans and that there are no human casualties in the ongoing war. The use of the term Processor to refer to the Eighty-Six pilots contributes to the Republic's lies.
For the Processors piloting the Juggernaut, there is little chance of surviving a hit. Since the Juggernaut was designed without any regard for pilot safety, there are no systems in place to protect the Processor inside. In fact, the cockpit of the Juggernaut is morbidly referred to by Processors as "the Guillotine" for its tendency to snap off from the rest of the machine when struck. The resulting injuries are often fatal because there are no cushions to protect the body of the Processor from striking against the insides of the metal cockpit. The Juggernaut is also a very fragile machine, unable to undergo rapid maneuvers for very long without breaking down, limiting the extent to which Processors can use the Juggernaut's maneuverability.
Owing to the sub-par specifications of the Juggernaut, a variety of tactics for dealing with the Legion have been passed down through the ranks of Processors. When a Legion incursion is spotted, the squadrons will set ambushes on the predicted path of the Legion units. Achieving the element of surprise is crucial because it allows the Juggernauts to target the weaker rear armor of the otherwise impenetrable Löwe as well as weaken the enemy without risk of damage.
Once the first volleys are fired, the Juggernauts employ fire and maneuver tactics to temporarily suppress the Legion and allow other Juggernauts to flank the enemy positions. Using team maneuvers is especially necessary against the heavy armoured Löwe, although a few exceptional Processors such as Shinei Nouzen are capable of handling a Löwe alone. These Processors utilize high mobility tactics to take on the Löwe alone, but due to the fact that the Juggernauts are poorly designed and made, the moves that the Processors execute can seriously damage the Juggernaut itself. This poses a lot of stress on the maintenance of the Juggernaut. This is the reason why the maintenance team of the Spearhead squadron always reserves two to three operational Juggernauts for Shin. Attacking from elevation is also a preferred method against the Löwes and Grauwolfs, both of which have difficulty elevating their weapons to target enemies above them.
The presence of the Legion's Scorpion artillery units is a significant danger to Juggernauts as their light armor can be pierced by shrapnel from the high-explosive shells. To prevent an artillery strike, the Juggernauts prioritize the elimination of the Ameise, which serves as forward artillery observers for the Scorpions.
Selecting terrain is another crucial aspect of tactics as soft ground like swamps can be a deathtrap for Juggernauts. Processors scrounge for maps from the surrounding ruins to determine favorable terrain.