This was a time of great technological innovation and ship builders were constantly trying to increase the thickness of the armour to resist the larger guns, while the gun manufacturers were developing ever larger guns to defeat the thicker armour. Very soon the gun sizes, projectiles and powder charges increased to the extent that the initial pressure inside the gun was too great when using prisms made from conventional gunpowder. To make the powder burn more slowly, ‘Cocoa powder’, so called from its cocoa-like colour, was developed.
The constituents of cocoa powder are: Saltpetre 79%, Charcoal 18% and Sulphur 3%. The charcoal was now made from straw carbonised by steam. Cocoa powder pressed into prisms is referred to as ‘Prism, Brown’, and this is the type of powder carried by HMS Colossus for her 12 inch Mk IV rifled breech loading guns.
A still slower burning powder was needed as guns increased size to 13.5 and 16.25 inches. Slow-burning Cocoa (SBC) was adapted from Prism, Brown by small alterations in its composition.
Colossus Battering Charge
The full charge for one of Colossus’ 12 inch guns is 295 lbs of Prism, Brown. This ‘battering’ charge, used when firing against armour, is made up of four cartridge bags made from silk cloth, each holding 73.75 lbs of Prism, Brown powder. If great penetrating power is not required, such as when firing against unarmoured ships, then a reduced or ‘three-quarters’ charge is used – three cartridges. For general practice a half charge would be used.
Silk bags are used since this material is entirely consumed when the cartridge is fired, otherwise a burning residue could be left which might cause a premature explosion when the next cartridge was placed in the gun.
Quick Firing Guns
In the late 1880’s a new threat emerged in the form of small fast torpedo boats (as advocated by the French ‘Jeune Ecole’ tactical thinkers), and to counter them, ships would need to carry a large number of small, fast firing guns. These ‘Quick Firing’ (QF) guns used a combined shell with attached cartridge case made from brass. However, they still used gunpowder, which produces an inordinate amount of smoke. The principle of quick firing would be negated if the target is hidden by the smoke of the first few shots. There was a need for a smokeless propellant.
As usual, it was the French who lead the way in developing a smokeless propellant. Britain followed by developing ‘Cordite’, and after long litigation on patent infringements, this propellant quickly replaced gunpowder in all major guns in the Royal Navy.