The irony of Bentick's sacrifice
Captain Loft is on his way to relieve Captain Bentick of his duties, but instead, Bentick gives his life to save Loft in an act of true sacrifice, accepting the ax that Alex swung so that Loft could prevail. That is ironic given the ordinary nature of their day, and the irony foreshadows that the townspeople are powerful humans with who pose a greater threat than a normal town of their kind. The townspeople are willing to risk their lives to kill Nazis.
The irony of Mayor Orden's role
Mayor Orden's role in times of peace is to act as a figurehead for the community. He serves the community by accepting the attention of the people, and then guiding them with his words and policies. But when the Nazis arrive, Orden's role because the ironic inverse. Instead of telling the people what to do, he gives them their sovereignty by claiming that they ought to decide for themselves what to do. He hopes they revolt. He is ironically passive.
Captain Tonder's emotions
Tonder is someone who doesn't quite feel peace about his role in the Nazi occupation. He sees that the place they interrupted was a peaceful, encouraging community of good folks who sacrifice for one another. That makes him ironically flippant about his own safety, because he longs for the community that he knows they have. Ironically, that makes him susceptible to the town's other side, the dark willingness to kill him. Molly kills him brutally, with scissors.
Competence and incompetence
The Germans are a scary force for the cast of this novel, because they have incredible resources and technologies. Then again, they lack moral fortitude in some occasions, and the townspeople have that in spades. So, although the Germans seem more competent, the shared love, sacrifice, and hard work of the town actually outweigh the German advantage. They are ironically competent at warfare, given they weapons.
The ironic ending
Orden is a kind of martyr for the town, because he was asked to stand up to the enemy who would certainly have him executed. They inevitably do have him executed, but not before he learns by hearing the distant bomb blasts that the resistance had successfully damaged the railroad, and therefore, the German supply chain. The siege would be rather likely to end if the Germans couldn't get supplies. Therefore, he knows that there is hope for the town, but ironically, he knows there is no hope for his own survival. He walks knowingly to his death.
