SV Marion Lightbody was a Russian full-rigged ship that was torpedoed by the Imperial German submarine U-20 in the Atlantic Ocean near the Fastnet Rock on 8 July 1915 while she was travelling from Valparaíso, Chile to Queenstown, Ireland while carrying a cargo of barley.

[1] Marion Lightbody was launched on 17 April 1888 and completed the same year at the Henderson D. & W. & Co. Ltd. shipyard in Meadowside, United Kingdom.

She was assessed at 2,242 gross register tons (GRT) and had four masts.

[2] Marion Lightbody was travelling from Valparaíso, Chile to Queenstown, Ireland while carrying a cargo of barley when on 8 July 1915, she was torpedoed by the Imperial German submarine U-20 in the Atlantic Ocean near the Fastnet Rock, just over a month after the same submarine had infamously torpedoed and sunk the RMS Lusitania in the same vicinity.

The 25 crewmen escaped the ship in a dinghy and were later picked up by a British patrol boat before being brought to Queenstown.