The M515E Spencer was a Coalition EMP weapon platform.
Electromagnetic pulse weaponry is not a new concept by the 28th century. The electronic-crippling effects were most infamously seen during the Collapse, when transistor-based computers were fried beyond repair by nuclear weaponry, leading to the technology’s abandonment. EMP weapons (now based on sonnematerial technology) were rediscovered in the 2500's when the pulses became powerful enough to disable vacuum tube technology and weaken energy shields. EMP technology would evolve throughout the centuries, becoming more compact and reusable as capacitors and generators shrunk in size. By the time of the gusano crusades, man-portable versions were available, if bulky. But EMP weapons always had very specific uses: they were used to weaken shields or disable them outright, but the latter only works if a shield generator is not protected by some outer armor, as is the case with most tanks but not with infantry. EMP weapons always had to be backed up with some other weapon system to finish off the targeted opponent; EMP weapons crippled opponents but could never kill them. To top it all off, EMP weapons were inaccurate and sometimes misfire, disabling nearby allied electronics. It was because of these flaws that EMP weapons were relegated to specialist units.
However, EMP came back into mainstream military thinking when reports started coming in about the M515 Shiloh. The Shiloh, notorious for its ammo cooking off, was infamous throughout the Coalition military. However, reports of targeted foes and surrounding armor being disabled accompanied reports of failure with a disturbing regularity. A study later showed that when the explosive charge in the Shiloh’s barrel cooked off, it destroyed the coilgun-based launch system and directed a particularly powerful electromagnetic pulse in the direction of the target (and, to a lesser extent, everywhere surrounding the vehicle). Additionally, rumors of new weapons platforms, human and xeno, throughout the Coalition intrigued military scientists who wanted relatively undamaged samples to study. The military saw a way to make EMP useful and to recycle the Shilohs it had already produced. Thus the M515E Spencer was born.
The Spencer is little different from its Shiloh parent, although it is lighter, less armored, has a weaker engine and a more powerful reactor. The gun and turret system of the Shiloh were replaced with the PDP-1 electromagnetic pulse cannon, the reason for the Spencer’s existence. The PDP-1 is constructed out of thick, hardened ceramic and tungsten-titanium, because it is not loaded with shells, but rather a basic coilgun system and a high explosive charge designed to destroy the coilgun when the weapon is fired. When detonated, the explosion sends out a massive electromagnetic pulse toward the enemy. A magnetic guidance system, similar to those found in sonnematerial weapons, helps guide the pulse to its target. The pulse can bore through most protective measures, disabling electronics, shields, weapons systems, engines and reactors. The target is left a sitting duck, ready to be captured by waiting Coalition troops. After firing, the whole coilgun and charge are reloaded into the PDP-1.
Despite its advantages, the Spencer has inherited the unpredictability of both its predecessor systems. The PDP-1 is infamous for its temperament: most of the time, the weapon fires perfectly, but at other times it can catastrophically fail. The explosive charge could be too powerful and blow apart the barrel and cook off the reactor, destroying the vehicle, killing the crew and sending an electromagnetic pulse out around the Spencer and hitting friend and foe alike, but mostly friend. Sometimes, the charge would refuse to blow and the gunner has to clear out a largely intact coilgun system from the barrel. The PDP-1 has also inherited the infamous inaccuracy of other EMP weapons. The engine is prone to random failure, for any reason and sometimes (to the chagrin of Army engineers) no discernible reason at all. The Spencer’s oversized reactor is just as fickle, sometimes refusing to start. This has led to the Spencer’s infamous reputation within the ranks and jokes about the cursed Shiloh platform, but soldiers still prefer it to the Shiloh. However the Spencer has only seen a limited production run, mostly to recycle Shiloh hulls, as Coalition high command dislikes its unreliability (while at the same time acknowledging its usefulness) and the simple fact that most missions call for destroyed enemy tanks, not disabled-to-be-captured enemy tanks. Spencers have found their place in specialist units and units that are both very lucky and very unlucky when it comes to requisition. Coalition military scientists are rumored to be working on a new model that uses more traditional EMP technology.