Disebabkan oleh kekerasan terlampau seramik yang digunakan, ia memberika rintangan terhadap jet shaped charge dan memecahkan penembus tenaga kinetik. The (pulverised) ceramic also strongly abrades any penetrator. Against lighter projectiles the hardness of the tiles causes a "shatter gap" effect: a higher velocity will within a certain velocity range (the "gap") not lead to a deeper penetration but destroy the projectile itself instead[11] . Because the ceramic is so brittle the entrance channel of a shaped charge jet is not smooth — as it would be when penetrating a metal — but ragged, causing extreme asymmetric pressures which disturb the geometry of the jet, on which its penetrative capabilities are critically dependent as its mass is relatively low. This initiates a vicious circle as the disturbed jet causes still greater irregularities in the ceramic, until in the end it is defeated. The newer composites, though tougher, optimise this effect as tiles made with them have a layered internal structure conducive to it, causing "crack deflection"[12]. This mechanism using the jet's own energy against it, has caused some to compare the effects of Chobham to those of reactive armour. This should not be confused with the effect used in many laminate armour of any kind: that of sandwiching an inert but soft elastic material such as rubber, between two of the armour plates. The impact of either a shaped charge jet or long-rod penetrator, after the first layer has been perforated and the rubber layer is being penetrated, will cause the rubber to deform and expand, so deforming both the back and front plates. Both attack methods will suffer from obstruction to their expected paths, so experiencing a greater thickness of armour than is there is nominally, thus lowering penetration. Also for rod penetrations, the transverse force experienced due to the deformation may cause the rod to shatter, bend, or just change its path, again lowering penetration.

Keberkesanan perisai Chobham dapat dilihat dalam Perang Teluk pada 1991 dan 2003, di mana tiada sebuah pun kereta kebal pihak bersekutu yang berjaya dimusnahkan oleh pasukan armor atau peluru berpandu anti kereta kebal Iraq. Dalam beberapa kes, kebanyakan kereta kebal yang berjaya dirosakkan oleh tembakan berulang kali menggunakan peluru dengan penembus tenaga kinetik atau peluru letupan kuat anti kereta kebal. Ini kerana jenis peluru yang digunakan oleh Iraq pada kereta kebal T-72, T-55 dan T-62 tidak berupaya untuk menembusi perisai hadapan kereta kebal pihak bersekutu. Harus diingatkan juga, tentera Iraq sebenarnya amat jarang berjaya menembak kereta kebal pihak bersekutu disebabkan oleh kekurangan latihan dan sistem optik dalaman. Sehingga kini, hanya 5-10 kereta kebal yang dilindungi oleh perisai Chobham berjaya dikalahkan oleh tembakan musuh dalam pertempuran, termasuk sebuah kereta kebal M1 Abrams yang ditembak di skirt sisi, di bawah cincin turet oleh RPG-7VR. Jet dari senjata RPG telah menembusi skirt perisai sisi dan perisai badan sisi, kemudian merentasi bahagian dalam kereta kebal dan akhirnya menembusi 1.5 hingga 2 inchi perisai badan di bahagian sebalah satu lagi.