Built by Scott's of Greenock as a minelayer, E51 was launched on 30th November 1916. With a surface tonnage of 662 tons (765 submerged), measuring 181 ft and with a beam of 22 ft, her two 800BHP Diesels could produce 14 knots and her two 420 BHP electric motors provided 9.5 knots submerged, although her service speed was a mere 3 knots. She layed extensive mine fields during World War One, one of which claimed the U-75 in December 1917. After the War she was eventually paid off and was broken up by the Wales Salvage Co in 1921.