as designated by Starfleet, was the original Illithidin fleet biomechanoid. Its devastating point blank grapple could kill a starship in a single attack. Its camouflage and stealth capabilities made it the quintessential predator. This is a resource 'ammunition' limited attack reserved for priority targets.
was the variant which introduced the Assassin Ghost* weapon system. It had small enough of an infrastructure that the new kraken-ships could carry both this weapon and the previous Slayer weapon. Apparently, however, previous Slayer variants could not be 'mutated' to carry this new weapon. In addition, an elite "circle of assassins" was required to operate the weapon.
was the final variant produced during the Illithidin War. Although their kraken-ships were undeniably deadly, strategists on both sides noticed a glaring deficiency. The illithids could have done far better during fleet engagements with concussion blast artillery support.
The Illithids copied, in concept, what the Federation and Klingons were innovating. The Thundercrush variant projects a powerful concussion blast projectile, not unlike the Federation's early phaser pulses. It's power level, of course was considerably greater. And like their enemies, they could unleash the energy either as a single large blast or as a carpet of cluster bombs. The direct hit of a Thundercrush isn't as damaging as the uni-beam attack (described later), but it can detonate just beyond starships which are keeping their damaged (or absent) deflectors away from the enemy.
Although development of this kraken-ship variant began mid-war, its introduction was accomplished in record time. The reason, Illithid super-ships (giant squid mobile starbase) already mounted the same weapon on a planet-killing scale. The price for this haste, however, was not having the lethal Slayer weapon built in. If the Illithidin intended to produce a variant which carried all previous weapons, it never became known. The war ended before they had the chance.
It was fortunate for the Federation that the Thundercrush variant wasn't produced in large numbers. By itself, most starships could fight off the Thundercrush. However, when supporting swarms of Slayers and Insidious, they effectively repulsed several Federation and Merc Fleet advances while inflicting extensive damage. The outcome of the war might have been delayed for years if there had been many more of them.
* Assassin Ghosts
The Federation first encountered this frightful weapon at the ancient Gorgon docks in deep space. The Illithids innovated a deadly telepathic projection weapon into their latest generation of Kraken-ships.
The system involved an Illithid "circle" of telepathic assassins who stood around what could vaguely be termed a 'scrying console'. The Kraken-ship's biomechanoid system would them amplify and project the circle's effect. This is about the only known 'downside' of the weapon. An Illithid circle of assassins is an elite group possessing years of experience. (In other words, you can't get there with six weeks of squidhead boot camp.)
Completely bypassing existing deflector shields, a phantasmal Illithid 'ghost' would manifest inside the starship. This phantasm not only provided the assassins a 'clairvoyance' of the surroundings, but it could unleash deadly, amplified mind strikes. The apparition was not fast moving, but it could go anywhere, containment fields and thick bulkheads not being a barrier.
This weapon created nothing less than a crisis for Federation starships. It was bad enough that a kraken-ship could kill a starship in a single, point blank attack. Starfleet was able to compensate to a degree by employing new tactics. Starships would travel in pairs, each ready to free the other if it was grappled. Also, ships with nine-niner speeds could eventually outrun or elude the hyperspace jumping kraken ships. However, that wouldn't help against the new ghosts.
It was discovered during combat that the Illithid assassins had difficulty keeping their phantasm on target if the victim ship maneuvered violently, continuously. While this did buy time, it meant that the evading starship could not outrun the kraken-ships. The Illithids would swarm in a loose sphere around their victims. As the victims twisted and turned violently to elude the ghosts, the kraken-ships would methodically jump to keep them at the center. Doing this, it wouldn't be necessary to grapple the victim ships. Conventional beam weapons would systematically pound the starships shields into pieces. The only resort would be to charge the attacking kraken-ships, which is exactly the kind of battle that the krakens want.
Another discovery was made, concerning this weapon system. Illithids have a more difficult time targeting inside 'unusual space' like wormholes and Tholian interspace. It isn't yet known if this is caused by a limitation in the weapon itself or if it is simply lack of ability in the Illithids currently using it.
To put it succinctly, if you run, the assassin ghosts will methodically exterminate your crew. If you maneuver violently, the Kraken-ships will swarm and tear you apart. To worsen the matter, cloaking a ship couldn't hide its crew from the mind-hunting Illithids. They and their ships could sense the presence of sentients.
Although Santa Fe Task force utilized a preplanned escape that the Illithids could not have anticipated, the Federation now realized that the entirety of Starfleet was in peril. The only desperate countermeasure to be tried was putting a Tasperian aboard each ship (humanoid race, devours mind energy). They had already proven themselves to be inimical to Illithids, even their arcanes. They were the one race within the Federation who could directly engage the apparitions. Having a Tasperian aboard ship had proven to be hard on the crews, but at this point there was no other option.
Federation scientists worked feverishly to analyze and counter the new threat. But without knowing anything about how the weapon functions, it amounted to so much groping at sensor readings and blind speculation. The Illithids had planned well. Considerable sensor-scrambling noise accompanied their apparitions.