The "Formidable" class of battleships were a three-ship class of pre-dreadnoughts designed by Sir William White and built for the Royal Navy in the late 1890s. The class comprised , , and . They were armed with a battery of four guns, they had top speed of , and they marked the adoption of Krupp armour in British battleship designs. The class formed the basis for the nearly identical of five ships, and those ships are sometimes included in the "Formidable" class. "Formidable", "Irresistible", and "Implacable" were built between 1898 and 1901 at the Portsmouth, Chatham, and Devonport Dockyards, respectively.