The film was inspired by Operation Alberich, a German withdrawal to new positions on the shorter and more easily defended Hindenburg Line that took place between 9 February and 20 March 1917.[68][69] However, the main and supporting characters all appear to be fictional.[70]
Contrary to the film's depiction, the number of Black soldiers serving directly in the British Army itself was unknown but negligible, as the Black population in Britain at the time remained small. Instead, the majority of Black troops who participated in the British war effort served in their own colonial regiments from Africa and the West Indies.[71] Over 15,000 men from the British West Indies enlisted in the military during the First World War, and by 1915 they were organised into the British West Indies Regiment.[72][73][74] The regiment served in the Middle Eastern theatre of World War I, including the Sinai and Palestine campaign and the Mesopotamian campaign.[75][76] Indian Sikhs would also have served in their own regiments as part of the British Indian Army, not as individuals in the ranks of British regiments and corps. By the end of 1915, the Indian infantry formations had been withdrawn from the Western Front and sent to the Middle East.[72][77]
The military historian Jeremy Banning was critical of the military tactics portrayed in the film, writing "It made no sense, as the film depicts, to have some battalions nine miles beyond the former German line and others seemingly unaware of whether this line was manned [...] As for the assault by the Devons, no unit would attack without adequate artillery support".[78]
