In his after-action report in 1917, British officer Lt. Col. D.M. Sole made a startling admission:

Sole distinguished between the men who preferred to avoid combat and the minority that bravely embraced it. In Killer Butterflies, historian James Roberts (PhD, Univ. of Worcester) takes a similar approach to understanding the experience of men in combat, while testing the theories of two of his field's pathfinders. Army combat veteran and historian S.L.A. Marshall found—using problematic research standards—that only 15–20 percent of US soldiers had fired their weapons in World War II.[1] Lieutenant Colonel (ret.) Dave Grossman, a psychologist, has buttressed this conclusion with additional evidence, both historical and psychological.[2] Roberts advances their work with a case study of a British division in World War I that shows the many ways infantrymen managed to avoid killing on the battlefield. He learned that soldiers were most likely to kill their enemy when they were part of groups or used distance weapons, for example a grenade rather than a bayonet.

Roberts selected the 19th Infantry Division (ID) for several reasons. It was comprised mostly of men with civilian backgrounds rather than long-serving military professionals, from diverse regions of Britain (xiii, 43). In other words, the division's personnel were neither exceptional nor outliers. To highlight the experience of the typical British soldier in World War I combat, Roberts turns to unit diaries and battle reports to minimize the "subjectivity and individuality" of the personal memoirs that, he believes, historians generally mine for evidence (xii).

The author finds that, of the weapons readily available to him, the typical infantryman favored grenades. But even then, only a small percentage of soldiers willingly used them. The experience of the 19th ID early in the war, particularly in raids, made its men the "fighting vanguard of the infantry" for the rest of the war. Nonetheless, even the division's most enthusiastic troops only made four raids over the course of six months (65). In part, this was because lower-ranking officers had little desire to see their "most committed trench fighters" killed or injured "before the main event" (79). Given the soldiers' liking for grenades, it is no surprise that the author identifies very few instances of bayonet attacks; this reflects the immense difficulty—both practically and psychologically—of killing at such close range with a knife or de facto spear.[3] He notes that combatants on both sides would surrender or flee to avoid killing at close quarters (83). Who, then, did the killing on the battlefield? Roberts argues that

The fact of infantrymen playing a largely "passive" role contradicts popular images of daring soldier-warriors.

A leitmotif of the book is that soldiers, from privates to battalion commanders, exercised individual agency in interpreting and following orders (or not), a circumstance facilitated by the effects of the fog of war on command and control on a dispersed battlefield. Roberts repeatedly shows that soldiers, especially out of sight of their officers, ceased to pursue their assigned objective in order to stay alive (61, 75). This predilection increased as casualty rates approached 30 percent (95). At the same time, officers—including battalion commanders—might defy higher authorities to preserve the lives of their men (90–92).

By 1917, however, the Army was attempting to reduce its soldiers' reluctance to fight and kill their enemy by implementing new formations in response to the German adoption of defense-in-depth tactics (134). This had organizational repercussions. Roberts colorfully describes the High Command's new stress on the platoon rather than the battalion or brigade: "if the infantry attack of 1916 had the appearance of a snake—a diminutive sharp end with a long tail—with the Bombers forming the head, then the 1917 creation was more akin to an octopus—with a multitude of arms reaching out to simultaneously assault the enemy" (133).

This shift represents just one change in the British Army's thinking. Nevertheless, it remained convinced that rifles and bayonets, not grenades, won wars (138, 148, 150). On the one hand, we may interpret this as a failure to grasp how men actually killed on the battlefield. On the other, as Roberts suggests, one could sometimes win without killing: "when the battlefield was stripped of its depersonalized killers, posturing the act of interpersonal combat could often be enough to win the war" (103).

James Roberts has not opened an altogether new perspective on the experience of war, and whether he fully supports his final conclusion—that human nature is not innately brutal—is not entirely clear (268). Still, he has certainly reinforced classic studies of the difficulties and psychological traumas of killing in combat, especially at close quarters. And his discerning reconstruction of the average soldier's experience of combat brings new insights into the British "face of battle" during World War I.