Why Greenboy shells were different

Green paint identified armour-piercing shells filled with shellite. Earlier British shells used sensitive lyddite fillings that could explode immediately on impact. Shellite mixed lyddite with dinitrophenol to reduce premature explosions. A 50:50 mixture produced insufficient fragmentation, so the first Greenboys used a 60:40 mixture; later shells used 70:30 for better fragmentation while retaining a margin against premature detonation. Stronger shell bodies and improved caps were also needed to carry the charge through armour. The intended result was damage inside machinery spaces or a magazine hit at long range. Colour coding helped crews distinguish the ammunition during storage and loading.