Passchendaele was the name of a town and of one of the bloodiest battles of World War I.
Public sentiment in a town in Canada was very much against men of military age who were not in the service, and a young man with the humble job of typesetter and the condition of asthma (and who was thus medically excused from the draft) was feeling the shame. He has the idea that he has a chance for excitement and glory in war. He wants to impress the girl he is engaged to, and more importantly, her father, a powerful and wealthy newspaper editor/publisher.
It is made clear later on in the movie that the powers-that-be recognized that those with asthma were less likely to survive the poison gas attacks on the part of the Germans for which this war was noted, and thus gave them medical exclusions from military service in WWI.
This movie did a good job of portraying the kind of war fever that went along with a country’s participation in this conflict; there was a public event at which men of draft age who were not in the military were publicly shamed, a woman of German ancestry had her house splattered with red paint and word “Hun”, in spite of the fact that she was a nurse in the war, and if you articulated the fact that there were certain drawbacks to war itself, every opportunity was taken to question your courage, your patriotism, and your sanity.
One person who was the target of this sort of thing was Sgt. Michael Dunn, a soldier sent back to Canada after having participated in a particularly bloody battle, with a diagnosis of “neurasthenia” or “shell shock”, now known as PTSD. He is seen recounting and regretting particularly graphic acts of violence. He appears to have a conscience, and this is a problem for those above him. The brilliant minds higher up on the chain of command kept him in the service and made him a recruiter. As such, he refused to recruit the young man whose asthma, according to regulations, precluded his participation. His immediate superior, who later lets the young man with asthma join in spite of the fact that it is unlikely that the asthma magically went away because the fiance’s father wrote a medical clearance, throws Dunn’s diagnosis in his face when he objects to the fact that the superior officer just broke his own rules for recruitment! Dunn later gets his own back. At a time when he has the element of surprise, Dunn threatens the superior officer and gets him to sign papers and send him back to the front, as he intends to serve as protector for the asthmatic boy, who is a relation to the nurse who is Dunn’s love interest. Before both of them leave to rejoin the war, Dunn helps the nurse kick her morphine habit, acquired during her last tour of duty. Dunn also socializes with a man with an amputated arm. The man lost the arm in an accident in a sawmill, “but the ladies don’t know that”, he says. Indeed, when the battle of Passchendaele itself is portrayed, it is shown that in this particular war, with its heavy use of artillery similar to that used in today’s wars, but without today’s medical technology, losing a limb in the war was not an uncommon fate. It helps that at one point in the movie there is a medical lecture concerning what artillery shells do to the human body. (It was, in fact, during World War I that the term “basket case” originated. It did not initially refer to the mental or psychological paralysis it implies today, but to someone who had managed to have every extremity shot away or damaged beyond repair, who had to be literally carried around in a basket.)
In spite of Dunn’s efforts to protect him, the boy with ashma dies, though not of asthma-related complications ensuing during a gas attack. In fact, the use of poison gas is suprisingly absent from the battlefield portrayal in the movie (perhaps because a heavy rain is falling for much of the time the armies are in the field).
He is strong enough to hand Dunn a neck chain and medal his sister gave him, which later hangs on the marker for Dunn’s grave.