In 1784 Lieutenant Shrapnel began developing, on his own time and at his own expense, an antipersonnel weapon composed of a hollow spherical projectile filled with shot and an explosive charge. It was designed to detonate in midair, scattering the shot and shell fragments.
Before Shrapnel's invention was adopted, artillery attacked infantry or cavalry with "canister" or "case," a tin container filled with iron balls. When the gun fired the container burst open at the muzzle. Up to 300 metres it caused heavy casualties. At longer ranges, common shell -- hollow cast iron spheres filled with gunpowder -- were used, but their fragmentation was poor.
Shrapnel's shells, filled with musket balls, released them above the target, allowing them to carry on with the "remaining velocity" of the shell. If the point on the trajectory at which the shells burst was well-chosen the balls would reach the target with lethal velocity. They were simply hollow cast-iron spheres filled with a mixture of balls and powder, with a crude time fuze, but they increased the effective range of case from 300 to about 1100 meters.
The British artillery adopted his invention in 1803 with universal enthusiasm. The Duke of Wellington used it beginning in 1808 against Napoleon, including the Battle of Waterloo, and wrote admiringly of its effectiveness.
As explosives improved it was found that a properly designed shell casing fragmented so effectively that additional shot was not required, and during World War II shrapnel, in the strict sense of the word, fell out of use.