HMS Irresistible—the fourth British Royal Navy ship of the name—was a Formidable-class pre-dreadnought battleship. The Formidable-class ships were developments of earlier British battleships, featuring the same battery of four 12-inch (305 mm) guns—albeit more powerful 40-calibre versions—and top speed of 19 knots of the preceding Canopus class, while adopting heavier armour protection. The ship was laid down in April 1898, was launched in December that year, and was completed in October 1901. Commissioned in 1902, she initially served with the Mediterranean Fleet until April 1908, when she was transferred to the Channel Fleet. Now outclassed with the emergence of the dreadnought class of ships, she entered service with the Home Fleet in 1911 following a refit. In 1912, she was assigned to the 5th Battle Squadron.

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 Formidable, Irresistible, and Implacable. They were armed with a battery of four 12-inch (305 mm) guns, they had top speed of 18 knots, and they marked the adoption of Krupp armour in British battleship designs. The class formed the basis for the nearly identical London class 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.