British explosive shells filled with Lyddite were initially designated "Common Lyddite" and beginning in 1896 were the first British generation of modern "high explosive" shells. Lyddite is picric acid fused at 280 °F and allowed to solidify, producing a much denser dark-yellow form which is not affected by moisture and is easier to detonate than the liquid form. Its French equivalent was "Melinite", Japanese equivalent was "Shimose". Common Lyddite shells "detonated" and fragmented into small pieces in all directions, with no incendiary effect. For maximum destructive effect the explosion needed to be delayed until the shell had penetrated its target.
Early shells had walls of the same thickness for the whole length, later shells had walls thicker at the base and thinning towards the nose. This was found to give greater strength and provide more space for explosive. Later shells had 4 c.r. heads, more pointed and hence streamlined than earlier 2 c.r.h. designs.
Proper detonation of a Lyddite shell would show black to grey smoke, or white from the steam of a water detonation. Yellow smoke indicated simple explosion rather than detonation, and failure to reliably detonate was a problem with Lyddite, especially in its earlier usage. To improve the detonation "exploders" with a small quantity of picric powder or even of TNT (in smaller shells, 3 pdr, 12 pdr - 4.7 inch) was loaded between the fuze and the main Lyddite filling or in a thin tube running through most of the shell's length.
Lyddite presented a major safety problem because it reacted dangerously with metal bases. This required that the interior of shells had to be varnished, the exterior had to be painted with leadless paint and the fuze-hole had to be made of a leadless alloy. Fuzes containing any lead could not be used with it.
When World War I began Britain was replacing Lyddite with modern "high explosive" (HE) such as TNT. After World War I the term "Common Lyddite" was dropped, and remaining stocks of Lyddite-filled shells were referred to as H.E. (or High Explosive) Shell Filled Lyddite. Hence "Common" faded from use, replaced by "HE" as the explosive shell designation.
Common Lyddite shells in British service were painted yellow, with a red ring behind the nose to indicate the shell had been filled.
For Shellite, a successor of Lyddite, see HE below.
Read more about this topic: List Of British Ordnance Terms
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