When the Capellan War started in 2255, the North American Union and Australio-Pacifica Coalition had the strongest militaries at the time, and were thus on the forefront of the Alliance war effort. Ground engagements fared only marginally better than naval battles, and the surfaces of the battlefield worlds were littered with the corpses and wreckage of hundreds of thousands of the Alliance’s best. It was in this brutal crucible that the NAU’s bureaucratic monstrosity of a war machine, the Arbalest battlewalker, was proven to be one of the worst-designed walkers in history. Both Capellan walkers and their giant bioweapon monstrosities (literally, the Capellans genetically engineered monsters right out of the worst nightmares of humanity) reduced the Arbalests to smoldering wreckage.
In answer to this, the NAU began a massive overhaul campaign to upgrade the Arbalest. With the Capellan advance on the Terran core systems, the American military did not have the time to re-invent the wheel and develop a new walker. So, they reviewed the battlefield feedback of the few surviving units and recoverable corpses they could. It was discovered that the Capellans had phenomenally strong shielding technology, but that they were surprisingly vulnerable to hyper-velocity projectiles such as those from Gauss weapons. Long considered a primitive weapon system, this new intelligence necessitated a radical overhauling and renewal of mass-driver technology.
Using next-generation gravitic accelerators instead of electromagnetic, these Gauss weapons- called Mass Accelerator Cannons, or “MAC guns”- were able to accelerate antimatter-containing projectiles to relativistic speeds (roughly .5 to .8C). As warships were refit with spinal mount MAC guns, a newer model of the Arbalest was produced that replaced the antiquated particle beam arms with a tri-barrel model containing two much more powerful PPCs and and a 150mm MAC gun. The hull was redesigned to be more streamlined and allow for non-sensor-dependent visability. The vulnerability to disruptor weapons (24th century equivalent to EMP) was drastically reduced, and the antiquated mortar system removed and replaced with a second Phalanx gun.
A massive 350mm MAC gun was added to the top for indirect firepower to replace the mortar, and updated missile racks were added to flank it.
After the war, new enemies emerged who were more broad-spectrum in their weaponry and defenses, and once again energy weapons came to the fore. The Model E Arbalest, the most recent incarnation of the bunch, evolved. The Phalanx systems were replaced with AP lancer emitters from the Australio-Pacifica Coalition, the anti-personnel chin gun was replaced with a powerful PPC, the left and right torso missile racks were sealed to prevent incoming shots cooking off the missiles, and a single rapid-fire missile port was added beside the cockpit on either side.
This allows for a high rate of fire while simultaneously protecting the missiles and the inner workings of the walker. The armor was upgraded with the latest atomically bonded metallic hydrogen carbon interweave battleplate, and the servos, reactor core, and leg actuators radically updated. The net result was a massively armored battlewalker that could move far faster and with far greater agility than its predecessors.
During the Freeman War for Independence, however, the faster and more agile Kodiak and Wolverine battlewalkers developed by the Free Systems Alliance proved to be more than a match for the Arbalest. Able to outflank the slower, ponderous American walker, the Freeman walkers picked off the weapon systems, sensors, and then the legs, disabling it and leaving the crew stuck in the massively armored hull with no choice but surrender. Seeing that speed and shields mattered more than armor for a battlewalker, the NAU began work on a replacement walker for the Arbalest. This walker, the Trebuchet, was still in the prototype stage when the Freeman War ended. As the truce was signed, and the Free Systems Alliance celebrated their newfound independence, the NAU began quietly replacing the Arbalest.
with the newer walkers. To this day, however, fully 43% of the NAU walker inventory is comprised of the venerable Arbalest E, and the ones sold off are quite popular with fringe colony militias.