After the miserable failures of the Arbalest battlewalker in the Freeman Rebellion, the North American Union was determined to update its ground forces’ equipment along with their naval upgrades. Due to the extremely high number of casualties inflicted by the heavily-armed, more agile and super-heavily-armoured Freemen, the NAU military engineers were tasked with developing a support walker capable of carrying substantial firepower and balancing mobility against defense effectively. The AW-23 Grizzly was the result.
If any one lesson was learned in the Freeman Rebellion- other than “do not orbitally bombard civilian population centers, it pisses your enemy off into a psychotic berserk rage and loses you popular support with other nations”- it was the effectiveness of a balance between agility and armour in prolonged engagements. When it came down to it the Freemen won seven out of every ten battles on the ground simply by being able to avoid more hits and endure more of a pounding than the much slower NAU units, who focused on armor at the expense of maneuverability. Tactical data gathered during the war gave the engineers at Kirkland-Drummond Military Robotics new insight into layering armour that pretty much everyone else had already figured out years prior.
Let it never be said that the Americans do things the easy way.
Prior to the development of the Grizzly, NAU walkers- especially the Arbalest- had a thick shell of armour over a relatively light superstructure. This was to allow for maximum lightness, ammunition bins, reactor cores, etc. However, once the outer shell was breached, the walkers were easily lit up by well-placed shots into the resulting holes. Freeman walkers, on the other hand, used Ahrugan design principles of a honeycomb superstructure, multiple layers of armour, and a decentralized infrastructure of a higher number of much smaller reactors spread throughout the walker rather than one monolithic one. They also integrated move-by-thought systems and a lighter, more agile frame to literally leap and dance around the slower, ponderous walkers of the NAU.
Unwilling or unable to attempt to duplicate the agility of the Freeman walkers, KDMR focused on their armour designs. Even when the outer shell of armour on a Freeman walker was breached, no vulnerable insta-kill shots presented themselves as the exposed area just led to more armour and a dense, honeycombed superstructure. The Americans literally had to beat down and tunnel their way through the walker at multiple points to disable them, and took considerable losses trying to do so.
KDMR used reverse-engineered battlefield wreckage of one of these Freeman walkers as the inspiration for their “new, advanced layered armour synthesis”, which is a fancy way of saying they copied the Freeman design and slapped their own patent on it. However, the overall design of the walker is most definitely NAU. Weapon systems are pretty standard- PPC arms and point-defense cannon under the cockpit, AP lancers for anti-missile defense, and LRM/SRM missile loadouts. One new weapon system, however, was first fielded on the Grizzly when it hit the fields in 2317- the HVMAC, or "Hive-Mack", High Volume Mass Accelerator Cannon.
Unlike conventional MACs- and, frankly, just about every Gauss weapon out there- the HVMAC does not attempt to use a gravitic pulse to through a huge, super-dense projectile at a target at half the speed of light. Instead, it throws a metric ass-tonne of smaller ones in a sheet of turine death at a rate of 200 rounds per second. The HVMAC mounted on the Grizzly is a double-barrel 30mm hypervelocity hose of death, according to anyone who gets in its way. Firing in bursts, the HVMAC can sweep an area, creating the projectile equivalent of the cutting sweep of a particle beam or AP lancer. It also completely buggers the flicker rate on most shields, bypassing them with a much higher percentage of rounds than conventional Gauss systems. The biggest drawback is obvious- it is an ammo-dependent weapon, and with its rate of fire it depletes its ammunition bins relatively quickly.