Narrated from the perspective of a teenage boy, Westall's novel offers a unique and engaging portrayal of the bombing of an English town during World War II. The constant exposure to the horrors of war forces the main characters in The Machine Gunners to mature prematurely. The narrator, Chas McGill, tries to navigate his chaotic world by asserting control over his small part of Garmouth. His inability to remain an innocent child amidst the terror leads him to transform from a naive collector of war memorabilia into a determined overseer of a hidden fortress.

Westall vividly and realistically depicts the bombings and their aftermath. Chas safely gathers shiny shrapnel from the streets but also encounters a dead, disfigured, and decaying German soldier. The realism in The Machine Gunners immerses readers in a world where living with the daily brutality of war is unavoidable. Death and destruction become so routine that Chas's Uncle George can extract dead children from the wreckage of a demolished building and then calmly sit down for lunch.

The novel also explores the irony of war, illustrating that the "enemy" is often just another person with similar emotions, concerns, and life experiences. The young characters in the story learn that love and respect for individuals hold more power than the hatred of symbolic enemies fueled by wartime propaganda. When they set their German prisoner, Rudi, free, the characters demonstrate an appreciation for love that surpasses political ideologies.