HMS Slinger was an experimental catapult ship operated by the Royal Navy during the First World War. After Royal Navy service from 1917 to 1919, she operated as a commercial cargo ship under the names SS Niki and SS Lingfield from 1920 until she sank in 1941.

Constructed as a hopper barge, HMS Slinger was purchased from her builder, Lobnitz and Company, Limited of Renfrew, Scotland, prior to completion. Intending to use her as a test bed for the shipborne launching of aircraft, the Royal Navy fitted her with a 60-foot (18.25-meter) compressed air catapult. HMS Slinger operated Fairey F.127 and Short 310 seaplanes during 1918.

Slinger was sold on 16 October 1919.

After her sale, the ship was converted into a merchant cargo ship. She entered commercial service under the Greek flag with Boyazides L, Brother & Company in 1920 as SS Niki. Niki was sold to Valsamakis & Company in 1934 and to Nomikos Petros in 1937, remaining under Greek ownership and registry throughout.^[1] On 28 July 1920, Niki arrived leaking at Liverpool and was beached at Tranmere. Cheshire.^[2] She was refloated, repaired, and returned to service.

Niki was sold to Valsamakis & Company in 1934 and to Nomikos Petros in 1937, remaining under Greek ownership and registry throughout.^[1] Later in 1937, Niki was sold to the Finchley Steamship Company and, under British registry, was renamed SS Lingfield. Lingfield continued to operate as a commercial cargo ship until 17 October 1941, when she collided with another vessel in the North Sea off the coast of Norfolk, England, and sank.^[1]

• Dittmar, F. J. & Colledge, J. J., "British Warships 1914-1919", (Ian Allan, London, 1972), ISBN 0-7110-0380-7

• royalnavyresearcharchive.org.uk H.M.S. SLINGER: The First H.M.S. SLINGER