Mills bomb

The Mills bomb emerged from a marine engineer's workshop in Birmingham to become the template for every hand grenade that followed. William Mills had spent decades working with metals—first as a shipbuilder's apprentice in Sunderland, then establishing Britain's first aluminum foundry in 1885, later supplying the motor-car industry from his Grove Street works. When trench warfare created desperate demand for reliable grenades in 1915, Mills possessed exactly the metalworking expertise the British Army needed.

The adjacent possible had been assembling for centuries. Byzantine Greek fire, Song Dynasty thunder crash bombs, seventeenth-century grenadiers throwing iron balls—all demonstrated the concept. But existing grenades were dangerous to their throwers. The British No. 1 grenade of 1908 armed before throwing; improvised jam tin grenades using lit fuses killed soldiers who held them too long. Leon Roland's Belgian design, rejected by the War Office in January 1915 for safety concerns, nonetheless showed Mills the path forward.

Mills's innovation was the safe grenade mechanism. A spring-loaded striker held under tension by a lever, the lever secured by a split pin—the grenade only armed after the lever released, which only happened after throwing. The four-second delay fuse gave enough time to throw but too little time for enemies to throw back. The grooved cast-iron body, often assumed to aid fragmentation, was actually designed for grip; Mills's own notes confirm it did not shatter along the segments.

Production reached 75 million units during World War I—more than all other Allied grenades combined. By 1917, every infantry soldier carried Mills bombs. The longest grenade battle, at Pozieres Heights on July 26-27, 1916, consumed 15,000 Mills bombs in 12.5 hours of continuous combat. The No. 36M variant, waterproofed for Mesopotamia in 1917, remained standard British issue until 1972. India's army retired the design only in August 2021—106 years after Mills filed his patent.