Testudo
The Testudo was an armoured personnel carrier (APC) that was used by the Imperial Army during the Great Crusade and the Horus Heresy. The Testudo was the Chimera's predecessor and apparently looked no different than today's APCs. The reason why the Testudo was phased out by the Chimera was because the Testudo was lightly armed and armored whereas the Chimera have the same function as the Testudo but with improved defenses and armoring. Another disadvantage of the Testudo was that it used solid rubber tires, which were less dependable than metal tracks later used by the Chimera which is stupid because replacing a flat tire takes less time and is so much more easier than replacing a destroyed track. Its disadvantage against the Chimera is also bizarre since the Testudo is one of the few Imperial vehicles that actually has sloped armor (If taken that its design is a modern APC) whereas the Chimera doesn't, meaning that the Testudo has more chance of surviving a hit from a anti-tank weapon due to its sloped armor ricocheting the shot while the Chimera has to eat a direct hit. Another example of GeeDubs failing again. The vehicle's main advantage over most other military vehicles of the time was its speed, as the absence of thick armor or heavy metal tracks allowed the vehicle to reach impressive speeds.
The weird part of the Testudo is that despite being lightly armored, it somehow weighed at a hefty 40 tons which is as heavy as a modern Main Battle Tank. Whether the Testudo was lightly armored in comparison to its weight or it was another example of developer oversight doing a typo is unknown. The Testudo is also one of the few wheeled vehicles of the Imperium, the other being the Tauros.
Weaponry
The Testudo was armed with an Autocannon mounted on a small turret, which was capable of turning a full 360 degrees, which allowed the vehicle to engage enemy units whether it was travelling towards them or fleeing. The Testudo's troop compartment was capable of carrying an entire infantry squad, up to twelve soldiers, yet lacked the Lasgun mounts featured on the Chimera. The troop compartment only had a single exit, a rear ramp wide enough to allow two soldiers to exit the vehicle side-by-side. The inside of the troop hold featured benches that ran the length of the hold, allowing the passengers to sit down. Near the front of the passenger hold were ammunition baskets that held the ammunition for the vehicle's turret-mounted Autocannon. It is unknown if the Testudo was able to be outfitted with other weapons or upgrades.