mainly forward but had little destructive effect. The system had major limitations: the thickness of the iron shell walls limited the available carrying capacity for bullets but provided little destructive capability, and the tube through the centre similarly reduced available space for bullets. In the 1870s William Armstrong provided a design with the bursting charge in the head and the shell wall made of steel and hence much thinner than previous cast-iron shrapnel shell walls. While the thinner shell wall and absence of a central tube allowed the shell to carry far more bullets, it had the disadvantage that the bursting charge separated the bullets from the shell casing by firing the case forward and at the same time slowing the bullets down as they were ejected through the base of the shell casing, rather than increasing their velocity. Britain adopted this solution for several smaller calibres (below 6-inch) but by World War I few if any such shells remained. The final shrapnel shell design, adopted in the 1880s, bore little similarity to Henry Shrapnel's original design other than its spherical bullets and time fuse. It used a much thinner forged steel shell case with a timer fuse in the nose and a tube running through the centre to convey the ignition flash to a gunpowder bursting charge in the shell base. The use of steel allowed a thinner shell wall, allowing space for many more bullets. It also withstood the force of the powder charge without shattering, so that the bullets were fired forward out of the shell case with increased velocity, much like a shotgun. This design came to be adopted by all countries and was in standard use when World War I began in 1914. During the 1880s, when both the old cast-iron and modern forged-steel shrapnel shell designs were in British service, British ordnance manuals referred to the older cast-iron design as "Boxer shrapnel", apparently to differentiate it from the modern steel design. The modern thin-walled forged-steel design made feasible shrapnel shells for howitzers, which had a much lower velocity than field guns, by using a larger gunpowder charge to accelerate the bullets forward on bursting. The ideal shrapnel design would have had a timer fuze in the shell base to avoid the need for a central tube, but this was not technically feasible due to the need to manually adjust the fuze before firing, and