Pictured above (crouching in the ruins to the lower right) is a two person sapper team hunting a tracked HK
The ruins of mankind's civilization were the play ground of a very dangerous, very final game where the stakes were the highest. As SKYNET's automated robotic killing machines moved through the ruins, demolishing every place that humans might find refuge or hide, there were dedicated teams of humans moving through the ruins hunting the machines. The smaller machines fell easy to simple ambush tactics at first, but SKYNET's neural net architecture soon allowed the machines to learn and they became much more deadly as they not only survived on the battlefield but they also instantly learned from mistakes made by other machines. What one machine knew, all eventually knew. Later designs incorporated multi-processor tactical arrays, with sub-processors in their weapon mounts allowing the weapons to "think" and act on their own, independent of the main processor array which was free to operate the main chassis. The larger HKs mounted individual dedicated tactical microprocessors in each of their turret sponsons, allowing each turret to operate independently and freeing up a large systems resource load off of the main processor of the HK (which could take direct control of any of its weapon systems at any time).
Those who hunted the Machines were known as colloquially as "sappers," a term taken from the long history of military engagements. Sappers were, by tradition, military engineers charged with breaching the enemy fortresses and strong points. The sappers of John Connor's army had little, if anything to do with field engineering and everything to do with high explosives for they were hunters, hunting the HKs out among the ruins of civilization and the ashes of the human race.
SKYNET's strong points and complexes were vast nightmarish installations created from an artificial intelligence that was not relegated to the confines of the human psyche. However, the most obvious strong points readily familiar to the human survivors were the lumbering mobile fortresses that SKYNET used to pacify and cleanse of all life entire sectors of territory. It was the responsibility of the human sapper teams to track and destroy these rumbling leviathans, a prelude to reducing the total projected strength of SKYNET in a region and thus weakening its hold on the current sector.
Resistance small unit tactics called for two person sapper teams to work the
ruins hunting the large HKs as this provided the greatest
amount of flexibility under the circumstances. The typical twelve person
squad was broken down into six, two person teams. Two teams would work
closely with each other, one team moving while the other team provided overwatch, in a leap frog type manner among the
ruins. The typical sub-team loadout was two M-25
plasma rifles (one with a M12 or variant of the M12 CRT flexy
sight), three M83 charges, spotter electronics and tight beam IR laser
communicators. Some teams carried thermal decoys which could occasionally
distract the HKs. Sapper teams, usually under
the command of a Sergeant, were sent out into the ruins with the goal of
destroying at least one HK per sub-team element (or a total of six HKs) and then returning, bringing back with them as much intel and recon as they could. Most of the larger HKs took two M83 charges to crack though a lucky team might
get a HK on the first try if they could use the local terrain to their
advantage or catch a HK that had been previously damaged but not repaired
Sometimes, the Machines would send out repair units to work on stricken or damaged Machines in the field. Advanced Resistance tactics called for damaging a heavy HK unit, one of some noted importance from a materials and resource aspect to SKYNET, and then waiting around to form an ambush for the repair units that SKYNET would usually dispatch. Extreme care had to be taken when carrying out this tactic due to the massive amount of close air support provided by SKYNET in the form of its HK Aerials. A damaged Machine was often a magnet for the HK Aerials which would circle around the disabled HK, searching the ruins, waiting and watching for any humans to try to finish off the disabled Machine. If enough care and patience was exercised on the part of the humans, they might be rewarded with the appearance of a large, automated repair Machine which would not only carry the automated tools to repair the disabled HK, but also replacement parts, any ammunition or fuel required to reload the HK, and vital other sources of parts, equipment and technology. The key to the windfall then relied on taking both Machines off line without a lot of collateral damage to either, a tricky prospect that sometimes involved precision sniper fire. The key point was that once the salvage operation had begun, time was of the essence. Any attack on either Machine would invariably lead to a rapid swarm of HK Aerials arriving on the scene or other heavy tracked HKs temporarily reassigned and moving in from their pacification sectors to assist in the recovery operation
A sapper's life was not glamorous. Hours, maybe days spent among the ruins, climbing over the broken remains of civilization, hiding behind cover hoping and praying that the Machines didn't detect you, or crawling slowly on your belly, one inch a minute, until you got within throwing distance of a HK, never moving so fast as to alert the sensors of the HK that you were there. The HKs possessed scan and track capacity in their automated gun mounts and could detect movement at close range instantly. Care and stealth had to be used when engaging a HK at such a close range and many sappers learned the hard, final way that carelessness in exposing your self during the throw could not only reveal your position but also give the HK time to terminate you and avoid the thrown charge. The heavy rapid fire weapons carried by the HKs were proof against most cover, no matter how thick so even if you ducked behind a wall, chances were that the power bolts from the HK's plasma guns would punch right through the wall and find you with little degradation to their killing power. The first lesson (and sometimes the last) that a sapper learned was to "throw without being seen."
Specialized general combat operations called for the sub-element sapper team to break even further into two, single elements and take up a position about six to ten meters from each other in a way that mutual support and communication could be carried out during the engagement. Working together, one charge would be thrown followed three to five seconds later by a second charge.
The first charge would be thrown into the path of the HK and would detonate under the machine or under the treads, smashing the drive assembly and disabling the HK. The second M83 charge would detonate under the machine as well, working to shatter the already weakened lower armor and wreck the machine totally. The third charge carried was as a backup in case the other two charges failed, for targets of opportunity or in case the team ran into something really big out in the ruins (which happened on more than one occasion).
Not every team made it back, attrition rates were high among the sapper teams and successful teams often formed close bonds between each other, learning and anticipating what the other would do in a situation until both team members moved and acted as one fluid unit.