Compound armour Compound armour was a type of armour used on warship s in the 1880s , developed in response to the emergence of armor - piercing shell s and the continual need for reliable protection with the increasing size in naval ordnance . Compound armour was a non - alloyed attempt to combine the benefits of two different metals — the hardness of steel with the toughness of iron — that would stand up to intense and repeated punishment in battle . By the end of the decade it had been rendered obsolete by nickel - steel armour . However , the general principle of compound iron was used for case - hardened armour , which replaced nickel - steel in the mid - 1890s and is still used today . Prior armours . Prior to the 1880s , all naval armour plating was made from uniform homogeneous wrought iron plates on top of several inches of teak to absorb the shock of projectile impact . A typical installation consisted of four to five inches of iron backed by thirty - six inches of solid wood timbers . Various experiments were carried out in order to improve the armour , which included breaking up the armour into a laminate of several thinner layers of iron with wood between them , as well as various experiments with cast vs . wrought iron . In all of these experiments , simple blocks of wrought iron consistently proved to provide the best protection . There had been several attempts to improve on iron with the addition of harder steels on the face , but these all failed for the same reason as the earlier laminate experiments ; the ability for the armour to spread sideways into its softer backing allowed it to be penetrated more easily . In the case of steel facing , the problem was that the steel would not adhere well to the underlying iron , allowing it to shift or separate entirely . In 1876 a competition was held by the Italian Navy at Spezia to trial new armours . By that point conventional iron armours had to be thick to stop contemporary naval artillery . The hands - down winner was a new soft steel from the French firm of Schneider et Cie , but this proved to be prone to breaking when stressed , making it less useful in naval applications . Compound armour was made from two different types of steel ; a very hard but brittle high - carbon steel front plate backed by a more elastic low - carbon wrought iron plate . The front plate was intended to break up an incoming shell , whilst the rear plate would catch any splinters and hold the armour together if the brittle front plate shattered . Steel plates positioned in front of iron plates had been tried unsuccessfully , for example in a trial by the Italian Navy at Spezia in 1876 . The problem of welding them together was solved independently by two Sheffield engineers , A . Wilson of John Brown & Company and J . D . Ellis of Cammell Laird . Wilson ' s technique , invented in 1877 , was to pour molten steel onto a wrought iron plate , whilst Ellis ' was to position the two plates close together and pour molten steel into the gap . In both cases , the plate formed was rolled down to about half of the original thickness . The steel front surface formed about one - third of the thickness of the plate . Compound armour was initially much better than either iron or steel plates , about a 25 % improvement . Throughout the decade continuous improvements were made in techniques for manufacturing both compound armour and steel armour . Nevertheless by the end of the decade all - steel plates had decisively edged ahead of compound armour , and the latter had become obsolete . Two major reasons for this were the introduction of forged chrome - steel shot in 1886 and the discovery of nickel - steel alloys in 1889 which proved particularly effective as armour plate . For instance , a trial by the French Navy at Gavre in 1880 found compound armour superior to all - steel plates . An 1884 trial in Copenhagen found that there was little difference between the two types , although compound armour was subsequently ordered by the Danish Navy , probably because it was cheaper . At the same time a similar trial to select the armour of the Italian battleship " Lepanto " saw compound armour plate demolished by two shots of the 10 - inch calibre guns which were to be fitted to the ship , whilst the same projectiles were shattered by 20 inches of French Creusot steel plate .