The CSM-10 (and its anti-personnel variants) provided SKYNET with a basic bipedal ground force unit but SKYNET needed a true soldier, a unit that could enter battle, engage the enemy and return for repair and redeployment if need be; a semi-autonomous weapon platform capable of direct, independent action as well as coordinated, controlled direction.  SKYNET was reviewing its design parameters; it needed a unit small enough to follow a average human through the ruins, a unit that was faster than a human and capable of overtaking and eliminating the target in a short order of time, thus allowing multiple target engagements without the threat of several targets eluding the unit while it concentrated on a single primary target.

The result of this need and the subsequent study gathered by SKYNET was the 300 Series HK Hunter Killer, dubbed a "Fast Walker" by the Resistance.  This was the first of SKYNET’s infamous “runnerpoddesigns, the later variants would include larger, tougher and far more powerful bipedal, tripedal and quadrapedal designs.

The 300 Series was a simple bipedal weapon platform, mounted on two oversized servo enhanced legs with large triple claw pads. The design of the large legs allowed the unit to balance on one leg while using the other leg for labor intensive work such as removing obstructions or smashing in doors and walls. The triple claw foot pads could not only be used in close combat (the claws could close inward, interlocking, with the force of hydraulics that could crush stone and tear steel) and for clearing debris / removing cover from Resistance units, but also provided the unit with superior traction on almost any surface. The claws could grip and dig in, allowing the full force of the hydraulic, myomer, and servo powered legs to literally catapult the unit forward in a high speed lope that no human could hope to match. The small size of the unit (2.5 meters tall, 1.5 meters wide) was matched only by its light weight (750kg). Its drive train could propel the unit to a running speed of 150kph on smooth terrain, about 80% of that on less than even terrain. It's small size also meant that Resistance units could no longer use ruined buildings and tunnels as cover from larger HK units as the 300 Series could follow the Resistance units where they chose to hide and since its balance was gyroscopically stabilized, it could both move and fire at the same time.

Honeycombed aluminum and hyperalloy reinforced chassis mounts held the miniature nuclear pulse reactor, the primary and redundant transmission units, and the electronics suite. In order to achieve a high volume of units, SKYNET had to retard the electronic self-autonomous capabilities of the unit slightly. SKYNET imparted a feral, almost animal intelligence into the 300 Series, resulting in an obedient soldier with the intelligence of a rabid guard dog and the single minded dedication of a machine. The 300 Series operated much in the manner of a crazed animal, smelling the kill. The 300 Series would squat dormant amid the rubble, sensors passive, until a target was acquired. The unit would then catapult itself out of its cover gaining speed, engaging what targets it acquired according to threat level and capability. 300 Series units were recorded by Scout units as actually tearing apart Resistance units rather than using energy ranged attacks; crushing resistance units with the 300 Series' claw feet, ripping and tearing other units apart, or using its own bipedal body to smash units against debris and building walls, crushing them.

The 300 Series shared many of the electronics of the Series 1200 Scout, and the capabilities of the Seeker. 300 Series units soon became known by a variety of descriptive names, the most commonly used being that of "Runner Pod". No amount of stealth protocol went into the design of the 300 Series and its servos whining as it covered the battlefield gave it a great psychological advantage over Resistance units.

The 300 Series was armored with hyperalloy, enough to withstand small caliber arms fire up to 7.62mm NATO. This was deemed adequate since at the time of the introduction of the 300 Series, the Resistance had not yet acquired massive stocks of phased plasma weaponry or the capacity to reproduce such weapons.  This changed when one of SKYNET's automated factories was hijacked by the Resistance. When the Resistance units became better armed, losses of the 300 Series series began to mount. Also, the limited intelligence of the semi-autonomous unit meant that it could be decoyed, or even tricked into tactically disadvantageous situations where it was quickly eliminated by smarter Resistance units.

300 Series units were armed with an internal mounted and stabilized Westinghouse M105A1 phased plasma gun, the modified version of a M95A1 rifle intended for use as an internally mounted gun in very light combat chassis designs. The M105A1 was mounted in a remote electric drive powered chin blister with a limited rotation of 70 degrees from the center line and a maximum elevation / deflection of plus or minus 30 degrees from the horizon.  This particular weapon was linked directly to the miniature nuclear reactor allowing almost infinite firing. The weapon mount was hydraulically stabilized so the 300 Series could fire at full stride.

The 300 Series was the first in SKYNET's series of fast open ground attack units, able to run down targets at a high rate of speed and engage.  The maneuverability of the 300 Series was reduced in close confines and it could not travel easily where biped based designs could (like underground or into dense ruins with narrow limits of accessibility.   Research and development as well as observed statistics and data from the field use of 300 Series units led to the eventual design and implementation of the T600 and T800 series.