In 2004, with ammunition running low, a British unit launched a bayonet charge toward a trench outside of Basra, Iraq, where some 100 members of the Mahdi Army militia were staging an attack. The British soldiers later said that though some of the insurgents were wounded in the bayonet charge itself, others were simply terrified into surrender.

Instilling such terror is at the heart of the philosophical argument for keeping bayonet training, historians say.

“Traditionally in the 20th century – certainly after World War I – bayonet training was basically designed to develop in soldiers aggressiveness, courage, and preparation for close combat,” says Richard Kohn, professor of military history at the University of North Carolina at Chapel Hill.

Bayonet training is, in short, used to undo socialization – to “basically to try to mitigate or eradicate the reluctance of human beings to kill each other,” Mr. Kohn says.