u/broadestsmiler

Yang's plan to take control over the Iserlohn Fortress should have failed by all accounts. The fact that he managed to identify Schönkopf and the Rosen Ritter and put his full trust in them to sneak into Iserlohn exclusively over a fight they had with Truniht's officers is absurd! Yang even mentions himself that he would be called a poor judge of character if things went wrong, as Murai correctly pointed out beforehand that a majority of Rosen Ritter commanders defected back to the Empire. What better way for Schönkopf to do this than loading him up with his Rosen Ritter regiment right over to an Empire fortress?!

Then you get two separate individuals from the Empire that attempt to enforce identity verification against the disguised Rosen Ritter from the Bremen, with the first guy getting tricked by Schönkopf coughing up fake blood and the second guy being dismissed by Stockhausen due to strange movements from the Alliance causing great concern. If either of these two guys actually managed to avoid getting tricked, how could the Rosen Ritter have fought back? The weapons were underneath Schönkopf, so they couldn't have been quick to retrieve. The Alliance would have been left hanging and could have had their fleet destroyed if Schönkopf didn't open the ports. Their strategy was also dependent on Admiral Stockhausen surrendering without a fight and his subordinates magnanimously laying down their arms (aside from that second officer who locks down the control systems).

The Rosen Ritter also figured out how to get to the control center of the fortress in less than two hours and get the ports back open, which seems implausible given the 60km diameter of Iserlohn fortress and the fact that they would have had very little prior knowledge of the layout of the fortress. (I think this time frame was actually closer to half an hour, I can't recall.) This seems incredibly implausible unless the distance from the command room to the control center was very short. The only way I could see this working is if one of the Rosen Ritter defected from Iserlohn previously or if info about the fortress was leaked in advance, which isn't outside the realm of possibility. However, you can actually see the Rosen Ritter looking at a map of the fortress inside of the command center!

Furthermore, the animosity between Admiral Stockhausen and Admiral Seeckt doesn't seem like something that the Alliance would have been privy to in advance. The fact that Admiral Seeckt ignored Oberstein's advice despite his sound reasoning was the only thing preventing the destruction of the Alliance fleet right then and there! Perhaps this animosity could have been leaked to the Alliance prior to the battle given the high status of both admirals, but this begs the question of why Yang never brought it up when discussing his battle plan initially. (Perhaps for screen time they cut this out? I'm not sure if the novels or the new anime adaption describe this further.)

To add even more salt to the wounds of this plan, why is it that none of the staff responsible for leading ships into the docking ports tried any sort of sabotage? Juan Lebello mentions a few episodes later that half a million prisoners of war were taken from Iserlohn Fortress, so why is it that not even one of them appeared to have the idea of causing issues while the Alliance ships were docking or once Alliance troops started piling in? Maybe there's an argument that there was something in the command center that could be used to hold other fortress troops hostage (e.g. venting out the atmosphere of their rooms), but this doesn't ever get mentioned as far as I am aware.

I think that there's quite a bit of plot armor and pure luck for Yang with this battle plan.