Machine guns proved extremely effective as defensive weapons, especially from their introduction in the late 19th century through the World Wars. Properly sited and protected, a few machine guns could stop or devastate attacks by forces many times their number.

Why they were so effective

Machine guns delivered continuous, rapid fire over beaten zones, allowing defenders to sweep trenches, open ground, and approach routes that attackers had to cross. In conflicts like the Russo‑Japanese War and the First World War, this firepower made frontal assaults across open ground extraordinarily costly, with attacking infantry “mown down” in large numbers.

Role in trench warfare

Their defensive power encouraged the extensive use of trenches, dugouts, and barbed wire so that small numbers of defenders could hold ground against repeated attacks. Armies learned to site guns to cover likely avenues of approach and wire obstacles with interlocking fields of fire, making many positions effectively impregnable to unsupported infantry assaults.

Limits and adaptations

Despite their defensive strength, machine guns were not unbeatable; artillery, better tactics (such as infiltration), and combined arms attacks gradually reduced the dominance of static machine‑gun defenses. In later conflicts, attackers used cover, maneuver, armor, and airpower to suppress or bypass fixed guns, so their relative advantage as purely defensive weapons declined.

Overall assessment

In sum, in the era of mass infantry assaults and limited mobility, the machine gun was arguably the quintessential defensive weapon, turning open‑ground attacks into massacres unless attackers adapted. As warfare evolved toward mobility and combined arms, machine guns remained important but became one element among many rather than the single dominant defensive tool.