Shellite originated after World War I as a development of lyddite (picric acid). For shellite, a successor of lyddite, see HE below. Firing Lyddite shells, or using trench mortars, was tried. The primary ammunition was HE (high explosive) shells filled with Amatol, Trotyl (TNT) or Lyddite. The British started replacing Lyddite with TNT in 1907. Lyddite presented a major safety problem because it reacted dangerously with metal bases.