The dramatic irony of trench warfare
In the graphic novel, the soldiers are often unaware of something the reader should know perfectly well: the death toll of the trench battles of WWI. Before WWI, soldiers knew that there was a chance that they would die, but in the trenches, that chance was way higher than ever before because of the increased efficiency and accuracy of human weaponry. They don't know when the battles begin that these will be the most horrifying, mind-bending battles in human history.
The irony of leadership
Because of the high stakes of warfare (especially in a newly nationalized Europe) neither side is given a real chance to understand and appreciate what new technology will mean for the future of warfare. Therefore, both sides often resorted to terrible leadership, sending people to certain death, simply because it was so difficult to believe machinery had become so powerful. The generals simply do not understand the gravity of new war machines.
The irony of progress
The irony of progress is that within the domain of warfare, technological advancement means higher death tolls. It means the more expedient loss of life. As the book shows, progress brings new forms of injury, weaponry, and new kinds of terror. Back home, technology means convenience and economic growth. But in the trenches, technology brings hell.
The irony of color
As the events in the book become more and more horrifying, the color drains from the pages, until the only colors are black, white, and sometimes red. This use of color gives the story a nightmarish, surreal quality, but that effect is ironic, since this story is factual and accurate (not a nightmare). This is a clever way of showing that to the people who were there, it was surreal and horrifying, so much so that they literally could not believe their eyes.
The irony of war and peace
By demonstrating war in all its gruesome truth, Tardi hopes to accomplish pacifistic goals, which is ironic but sensible. By reminding people visually what the actual events looked like, Tardi is forcing us to understand the truth about human nature, about human history, and about the dangers of technologically sophisticated warfare.
