Engen's scholarly work on combat effectiveness during World War Two addresses research, assumptions and beliefs long held. These are that shockingly high numbers of soldiers fail to fire their weapon in combat, that the Wehrmacht and Waffen SS were superior soldiers, and that the Allies only won the Second World War through sheer numbers and greater material resources. This largely challenges the work of Samuel Lyman Atwood Marshall who arrived at the conclusion that only 15-25% of combat infantryman fire their weapon. Marshall also advanced the theory that men had a natural "inner resistance" to take the life of another.
Marshall claimed to have conducted his research from World War 1 through the war in Vietnam. As such, his conclusions have been elevated to accepted doctrine which Engen argues is both deceptive and dangerous to the study of men-in-arms. Ferguson's War of the World, Bourke's An Intimate History of Killing, Dwyer's War, and Grossman's On Killing and On Combat all reference and advance Marshall's theories furthering a potential grand inaccuracy. Engen has combed through interviews with Canadian officers following WW2 and arrived at evidence that strongly overturns Marshall's longstanding work. Fascinating aspects include:
- espoused values versus values-in-use to explain how men can kill
- the impact of the Great War, namely the social acceptance of mass killing
- volunteer versus conscripted troops in terms of effectiveness (on a relative basis Canada had the largest volunteer force of the Western powers)
- antiquated warfare doctrine practiced by the Canadian General Staff
- limitations of both artillery and armour without infantry support
He concludes that, "Canadian soldiers displayed initiative and imagination in battle and proved to be capable warriors, frequently outfighting their enemies in close combat." Incredibly, Canadian infantry rifle companies made up less than 15% of the army's strength but accounted for 70% of all casualties. This would suggest that they got good at their job. Part of their combat effectiveness was actually fire discipline which turns Marshall's research on its head. Engen's work shows how Marshall's claims are considerably inconsistent with the Canadian experience.