The Duncan class was a class of six pre-dreadnought battleships built for the Royal Navy in the early 1900s. The six ships—HMS Duncan, HMS Albemarle, HMS Cornwallis, HMS Exmouth, HMS Montagu, and HMS Russell—were ordered in response to Russian naval building, specifically the fast second-class battleships of the Peresvet class, which they were specifically to counter. The foremost design consideration was a high top speed to match the rumoured top speed of 19 knots of the Russian ships while maintaining the same battery of 12-inch (300 mm) guns and keeping displacement from growing. This forced significant compromises in armour protection, though the ships adopted a revised system of protection for the bow, which was copied in other designs like the London class.

Pre-dreadnought battleships were sea-going battleships built from the mid- to late- 1880s to the early 1900s. Their designs were conceived before the appearance of HMS Dreadnought in 1906 and their classification as "pre-dreadnought" is retrospectively applied. In their day, they were simply known as "battleships" or else more rank-specific terms such as "first-class battleship" and so forth. The pre-dreadnought battleships were the pre-eminent warships of their time and replaced the ironclad battleships of the 1870s and 1880s.