The armour configuration of the first western tanks using Chobham armour was optimised to defeat shaped charges as guided missiles were seen as the greatest threat. In the eighties however they began to face the improved Soviet 3BM-32, then 3BM-42 kinetic energy penetrators which the ceramic layer was not particularly effective against: the original ceramics had a resistance against penetrators of about a third compared to that against HEAT rounds; for the newest composites it is about one-tenth. A typical example, the 3BM-42 is a segmented projectile which frontal segments are sacrificed in expanding the NERA plates in the front of the armour array, leaving a hole for the rear segment to strike the ceramic with full efficiency. For this reason many modern designs include additional layers of heavy metals to add more density to the overall armour package.