In contrast, a high-explosive shell contains a relatively large and energetic secondary charge of high explosive (known as a burster charge) which, when ignited by the fuse, produces a powerful supersonic shock wave that shatters the entire shell casing into many fragments that fly in all directions. The use of high explosives with a fragmenting case improves efficiency as well as propelling a larger number of fragments at a higher velocity over a much wider area (40-60 times the diameter of the shell), giving high-explosive shells a vastly superior battlefield lethality that was largely impossible before the Industrial Era. World War I was the first major conflict in which HE shells were the dominant form of artillery; the failure to adapt infantry tactics to the massive increase in lethality they produced was a major element in producing the ghastly subterranean stalemate conditions of trench warfare, in which neither side could risk movement above ground without the guarantee of instant casualties from the constant, indiscriminate hail of HE shell fragments.