 By the late 1850s, Britain and France were locked in an arms race.A new generation of increasingly accurate and powerful guns had been developed (of the Rifled Muzzle Loader (RML) and Rifled Breech Loader (RBL) types), mounted on fast-moving, manoueuvrable steam-powered ironclad warships such as the French "La Gloire" and the British .Britain's coastal defences had not been substantially upgraded since the Napoleonic Wars and the country's existing fortifications were largely obsolete.