HMS E3 was the third E-class submarines to be constructed, built at Barrow by Vickers in 1911-1912. Built with compartmentalisation and endurance not previously achievable, these were the best submarines in the Royal Navy at the start of the First World War. She was sunk in the first ever successful attack on one submarine by another, when she was torpedoed on 18 October 1914 by U-27.