The B-class was a class of 11 submarines, built by Vickers in Barrow-in-Furness for the Royal Navy, and launched in 1904–06. One boat was sunk by a collision in 1912, but the remainder served in World War I. Three boats protected the transfer of the British Expeditionary Force to France in 1914, but were soon relegated to local defence and training duties. Six submarines were in the Mediterranean when the war began and were quickly sent to the Dardanelles to prevent a breakout by the German battlecruiser SMS Goeben and the light cruiser SMS Breslau into the Eastern Mediterranean. B11 ventured into the Dardanelles in December 1914 and sank the elderly Turkish ironclad Mesudiye.

The British C-class submarines were the last class of petrol engined submarines of the Royal Navy and marked the end of the development of the Holland class in the Royal Navy. Thirty-eight were constructed between 1905 and 1910 and they served through World War I.