Chieftain tank
The most common type of composite armour today is Chobham armour, first developed and used by the British in the experimental FV 4211 tank, which was based on Chieftain tank components. Chobham uses multiple non-explosive reactive armor plates (NERA), which sandwiches a layer of elastomer (like rubber) between two plates of steel armour. This was shown to dramatically increase the resistance to HEAT projectiles, even in comparison to other composite armour designs. Chobham was such an improvement that it was soon used on the new U.S. M1 Abrams main battle tank (MBT) as well. The need to mount multiple angles plates, along with an outer steel layer to protect the armor array, gives the Challenger and Abrams their "slab sided" look.