Although a work of fiction, the novel purports to be as historically accurate as possible. Notable themes are the development of aerial warfare tactics, the Hawker Hurricane fighter, the British class system within its military, and the difficulty of training and integrating new pilots during wartime. The novel was controversial because it challenged the greatly inflated British claims of Luftwaffe aircraft destroyed during the Battle of Britain, and theorized that the air battle was "irrelevant" to the possibility of a Nazi invasion of Britain following the fall of France. Robinson defends his work by stating that the truth of "faults and deficiencies" only enhances admiration for the courage and resilience of RAF pilots.