M-29 Grizzly Heavy Infantry Fighting Vehicle
Origins
When the Systems Alliance Navy was formed in 2149, they required equipment and vehicles to operate. Naturally, the UNN who been responsible for policing the Sol system prior to the discovery of the Martian ruins began supplying the navy with starships.
But the UNN didn't operate a surface combat force and the Alliance needed armoured vehicles to support ground operations, so they purchased them from the United North American States government. The UNAS' M-25 Rhino Main Battle Tank was a powerful, heavily armed tank purchased by the Alliance as the centerpiece of their surface combat operations. However, despite the Rhino representing the pinnacle of tank design at the time, it's shortcomings became apparent very early on. The tank's size combined with the challenges associated with the terrain and environment of extraterrestrial planet's made deployment of Rhinos a logistical nightmare.
As such, the tank never saw much action beyond Earth's soil and was relegated to more of a symbolic role as it's intended role was taken up by smaller, lighter, more mobile armoured fighting vehicles like IFVs and APCs, which could be deployed to a planet easier and operate more effectively, especially in independent operations. However, even these had their flaws. As primarily Infantry suport vehicles, these vehicles lacked the punch or endurance to stand up against sustained ground combat. They also lacked any built-in life support systems. An issue that became more prominent as the years past and the Alliance found themselves deployed more and more often to worlds with hostile environments and non-breathable atmospheres, forcing them to rely on the limited air supply of their vac-suits and hardsuits. Which in turn limited the range and duration of many operations.
As a fledgling interplanetary military force, it became apparent that a new vehicle was needed to support interplanetary operations and become the mainstay of the Navy. But with the the age of the tank seemingly at an end, they knew that whatever it was going to be, it wasn't going to be an MBT.
Overview
The M-29 Grizzly was a 6-wheeled Heavy Infantry Fighting Vehicle built by Devlon Industries in 2155 as a successor to the almost obsolete M-25 Rhino Main Battle Tank.
As early as 2152, the Alliance began exploring designs for a combat vehicle best suited for their needs. Over a dozen military contractors submitted their own designs, but it wasn't until Devlon Industries (An Earth-based megacorporation known for their reliable military equipment and high-quality environmental protection equipment) presented the Alliance with the design of the Grizzly in 2155 that the Alliance accept the design. Awarding them the contract to produce two dozen Grizzlies with more to come.
The large, by IFV standards, M-29 Grizzly combined the firepower and protection of a Main Battle Tank with the speed, range, flexibility and troop carrying capability of an Infantry Fighting Vehicle. Along with the addition of an environmentally sealed interior and on-board life support system.
Nicknamed the "Battle Taxi" by Alliance marines the M-29 Grizzly would go on to serve as the centerpiece of Alliance groud campaigns and surface operations for almost three decades. Serving most notably during the First Contact War.
However, while excellent in long-term planetary campaigns, the Grizzly had issues of it's own. Most notably was it's size. Though significantly smaller than the previous Rhino, the Grizzly was still massive, making it slow and cumbersome to drive as it struggled to keep pace with other military vehicles. And in an era where speed became the deciding factor for Alliance victories, a tactic which hinged on rapid-surface deployment, the Grizzly was beginning to fall behind.
By the start of the 2180s, the Alliance contracted Devlon Industries to redesign the Grizzly. To condense the design into something more compact and versatile, while sacrificing as little of the vehicle's firepower and protection as possible.
The result was the M-35 Mako, which entered service in early 2183 and would go on to entirely replace the Grizzly by the end of the year.
Chassis
The M-29 Grizzly was 14 meters long, 5.8 meters wide and 2.3 meters tall, not including it's turret or antenna that would bring it up to 8 meters tall. With a weight of 33 tonnes.
It's central chassis was divided into two compartments capable of pivoting independently from each other. A driver compartment at the front along with the power pack and the forward two wheels, and a troop compartment at the rear along with the four rear wheels and an automated turreted mass accelerator cannon on the roof, remotely controlled by a gunner in the driver compartment assisted by the VI.
Due to the immense length of the vehicle, the front two wheels of the Grizzly were mounted on extendable arms that could raise or lower the drive compartment independently from the rest of the vehicle to cope with steep inclines.
The drive compartment came to a sharp nose with headlights on the end. A self-tinting windscreen was located on the "chin" of the vehicle.
Wheels
The Grizzly was a 6-wheel drive combat vehicle. Each wheel featured their own independent in-hub wheel motors and VI controlled suspension to keep all 6 wheels on the ground at all times.
The wheels themselves were a colossal 2 meters in diameter and 1.7 meters in width. With armoured wheel covers and alloy track tires that made them almost indestructible.
To prevent unintended spin, the onboard VI could automatically adjust the traction and power to each wheel to ensure perfect distribution of power no matter the terrain or surface.
Power and Propulsion
The Grizzly was an electric vehicle powered by a hydrogen-oxygen power cell which feeds power to the motors in each of the 6 wheels and powers the other core systems, including the eezo drive, shields and weapon systems.
A power cell consists of two electrodes, a negative electrode (or anode) and a positive electrode (or cathode), sandwiched around an electrolyte. Hydrogen is fed to the anode, and oxygen is fed to the cathode. A catalyst at the anode separates hydrogen molecules into protons and electrons, which take different paths to the cathode. The electrons go through an external circuit, creating a flow of electricity. The protons migrate through the electrolyte to the cathode, where they unite with oxygen and the electrons to produce water and heat. This engine design is standard with most air and ground based vehicles in the Alliance, having replaced fossil-fuel engines over 70 years ago.
The Grizzly carried a small eezo drive core. Eezo drives consist of a core of element zero. An electric current from the power cell is run through the element zero to generate energy fields capable of altering the mass of a bubble of space-time. A positive current increases mass and a negative current decreases mass. This was used to power shields, weapons and the mass effect fields. As the Grizzly drove the onboard V.I. constantly adjusted the weight of the vehicle to maintain the best balance between speed and grip possible no matter the terrain or planetary gravity.
Armour Plating
The hull was covered with heavy ablative ceramic composite armour plating providing up to 120 millimeters of protection against directed energy weapons like lasers that weren't blocked by the shields, by boiling away when heated. The vaporised armour material scattered the DEW beam, rendering it ineffective.
It was intentionally sloped back with very few flat surfaces facing forward. This helped against directed energy weapons by increasing the surface area a beam would hit, distributing the heat. It also put the kinetic barrier emitters at an angle, meaning that unless the projectile was traveling at a perpendicular angle to the surface, it was more likely that the kinetic barriers would slap it aside, rather than absorb the energy directly, reducing shield strain.
Shields
The Grizzly featured a kinetic barrier array linked to a Model 3 kinetic barrier shield generator.
The exterior layer of the hull was covered in tiny emitters spaced evenly across the armour plates. An object with mass traveling above a certain velocity would have trigged the barrier's reflex system, generating a localised repulsive mass effect field around the point of impact, deflecting it.
This was not without risk, however. The emitters themselves could only repel objects up to a limit. Sufficiently massive objects traveling at a high enough velocity could pass through the barriers unimpeded. Additionally, the kinetic barrier generator took power from the vehicle's mass effect drive. Even if the projectiles did not penetrate, consistent impacts could put strain on the generator, this strain in turn was carried back to the drive. To prevent potential drive failure, the drive was designed to temporarily shutdown power to the shields until the field stabilises once again. The sudden, abrupt shutdown of the generator caused all emitters to discharge residual energy build-up. Triggering the characteristics "shattering" effect.
This allowed the vehicle to withstand impacts from kinetic-based weapons, but didn't do anything against Directed Energy Weapons such as lasers.
The strength of the kinetic barrier depends on the size of the mass effect drive, the amount of element zero used and overall design of the drive and generator. The more powerful the mass effect fields the drive generates, the more powerful the shields can be. The Grizzly's knetic barriers were only resistant to modern anti-tank weapons upto a limit.
Crew Compartments
The Grizzly had a crew capacity of eight. A driver and gunner in the drive compartment and six passengers in the troop compartment. Separated from each other by a sealed door in the middle. A manually operated hatch on the roof of the drive compartment was used to enter and exit the vehicle.
The troop compartment also held ammo stores and rations for long-term ground operations.
Both compartments were environmentally sealed and pressurised. The hull was rated for atmospheric pressures ranging from 0 upto over 300 Earth atmospheres. And could withstand extreme temperatures of from at least -200 degrees Celsius upto 400 degrees Celsius.
Armament
The turret housed the Grizzly's main gun, as well as targeting sensors and an autoloader fed by an ammo magazine stored just below the turret. The turret could perform a full 360 degree rotation in around 4 seconds and had a barrel elevation of 60 degrees and a depression of -30 degrees.
The gun in question was the M-434 180 millimeter Subordinate Mass Accelerator cannon. Mass accelerators reduce the mass of a solid metal slug then accelerate it to high velocities using precisely controlled electromagnetic attraction and repulsion. Mass accelerators are able to achieve such high velocities that slugs had to be designed to deform on impact to increase the amount of energy transferred to the target. Otherwise it would pass right through, doing minimal damage. The M-434 fired a 9 kg 70x294 mm sub-calibre armour piercing round at 25 km/s every 5 seconds
Virtual Intelligence
The Grizzly also represented a massive advancement in combat vehicle technology as the first human military vehicle to have an integrated virtual intelligence. Designated as the Hector-class Combat VI, the Grizzly's virtual intelligence was an integral part of the vehicle's operation. Responsible for controlling the suspension, maintaining and adjusting the shielding and providing steering assist.
The VI was vital for the operation of the main gun. Responsible for loading, aiming and firing the main gun under instruction from the gunner in the drive compartment, who first designated targets and then waited a moment for the VI to aim the turret. Sensors in the turret calculated the range, wind speed, wind direction, atmospheric pressure and humidity and adjusted the barrel trajectory slightly to compensate before providing the gunner with a target lock. This all happened in the less than two seconds it took for the turret to rotate and find it's target. Once receiving the target lock, the act of actually firing the gun was left to the gunner's discretion. This design ensured that the Grizzly rarely misses it's target, no matter how fast it or it's target were moving.
The VI also operated and administrated an array of sensors on the exterior hull, including thermal sensors, motion detectors, ground-penetating radar and laser targeting detectors to warn against incoming laser guided munitions.
Variants
The civilian VT7 Armoured Personnel Carrier was a stripped down variant of the M-29 sold on the civilian market. The VT7 lacked the armament and military-grade systems of the M-29. The Hector-class VI was also replaced with the simpler and cheaper Edna-class VI.