The premise of the series, the gore, and the amount of death and destruction the Ubers cause.
Battleship Zero, the Third Reich's gruesomely unsuccessful first attempt at creating a battleship-class Uber.
On a more psychological level, the Uber spies. They can be anywhere, disguised as anyone, and if one takes your place, not even your own loved ones would know the difference until it was too late...
What happened to Patrick O'Connor, the first Allied Battleship. He managed to get Sieglinde into a choke hold and was this close to killing her. Yet she managed to escape by first ripping off both of Patrick's arms and then horribly mutating his entire upper body into a grotesque monstrosity of bones and flesh that looked akin to a body mid-explosion. The worst part? Patrick was still alive during all of this.
The pile of "failed experiments" that Scheele sculpted. Imagine having a poor facsimile of Hitler's face burned onto your skull while you're still alive. The last successful test begged for death.
The burning of Antwerp. Two killed citizens seem to have been welded together by the halo attack.
Uber: Invasion opens with the first German attack on American soil and its aftermath.
Several survivors relate their testimonies: one badly burned scientist reminisces how he saw several people on fire in the darkest of night. Two soldiers tell how they barely survived an direct encounter with the Ubers, only for a Reveal Shot to show that one of them was cut in half.
A little girl recounts how she barely survived her house's burning and trying to save another girl while her arms were dissolving, just before dying of epilepsy in front of the camera.
What really nails the crushing sense of hopelessness is that the reporter covering the incident comments how can the survivors be so silent, if he were them, he would have been screaming.
Leah Cohen has a nightmare where she's still a young girl, running across a field of Jewish skulls, being pursued by a gas mask-wearing Siegmund and Sieglinde, before she runs into a dead soldier she befriended with a half-melted face, asking her why she didn't save him.
Finding out that Siegfried is only fourteen years old at the time of his death. The Nazis took him—and admittedly, he was seriously messed up to begin with—and mutated him into a Battleship-class Uber that could gleefully commit the acts he did, warping his mind even further than it was and denying him his childhood, wretched though it might have been.
Issue #16 finally shows what happens when a Battleship turned against their masters. After apparently dying in a Unfriendly Fire incident, Katyusha mercilessly levels Moscow to the ground before Stalin's eyes. The carnage was so horrifying that he began to cry. She initially spares him with the intent of personally executing him in the most karmic manner - turning him into a statue made of Woden's Blood. Finally, she installs herself in power over Russia and effectively destroys the Soviet Union.
We get to see the effects of a nuke on a Battleship-class Uber such as Siegmund. Remember what happened to Patrick O'Connor? This is ten times worse, since his body is melted into the ground in a pile of flesh that could be swiped with a mop. And yes, he is still conscious while this happens. And unlike O'Connor, its impossible to euthanize him in this state.
Battleships are shown to be able to heal themselves from horrific injuries, if given enough time and support. Problem: He’s so radioactive nobody can get close enough to feed him or give him water, even if anyone wanted to. So: melted, blasted, radioactive, still alive, and very slowly dying of thirst and starvation. He’ll probably be entombed to avoid contaminating everything around him, so add slow suffocation to the list.
