On 5 September 1914 U-21, commanded by Kapitänleutnant Otto Hersing, torpedoed and sank the scout cruiser HMS Pathfinder, leader of the Eighth Destroyer Flotilla, off St Abbs Head on the south east coast of Scotland. This was the first time that a submarine had sunk a ship using a motor powered torpedo.
The Confederate submarine H. L. Hunley sank the sloop USS Housatonic during the American Civil War by attaching a spar torpedo to her hull. The word torpedo was then used to describe weapons that would now be called mines. A spar torpedo is more akin to a limpet mine than to a twentieth or twentieth century torpedo.
The sea was very rough, meaning that U-21 was plunging up and down, but Hersing succeeded in hitting his target with a single torpedo. It struck Pathfinder under her forward funnel. Her forward magazine blew up and she sank within four minutes, too quickly for her to launch her boats.
Most of her crew went down with Pathfinder, but sources differ on the exact number of men killed and saved. A BBC report on the laying of a wreath on the wreck on the 100th anniversary of the sinking by divers says that 18 survived and 250 died. Wikipedia names 18 survivors, but adds two civilian canteen assistants to the total on board, giving 252 dead. R. H. Gibson and Maurice Prendergast write in The German Submarine War that 259 were lost. The website Naval History gives 278 on board, of whom 16 survived. Elsewhere it lists the casualties.
The survivors included Pathfinder’s captain, Francis Martin-Leake, who was wounded. He was adamant that his ship had been struck by a torpedo, although it had at first been thought that she had been struck by a mine. His report can be found on the website The Dreadnought Project.
The 7 September 1914 edition of The Scotsman newspaper reported an official press release that stated that Pathfinder had struck a mine. The next day it printed an eye witness account that talked of ‘the diabolical policy pursued by Germany in strewing the sea with floating mines in tracts where peaceful fishermen are as likely as the crews of warships to be the victims.’
By 15 September, however, The Scotsman was reporting that Pathfinder had been sunk by a torpedo fired by a U-boat that it claimed wrongly to have been sunk by the ‘brilliant British gunnery’ of a number of cruisers.
‘Another eye witness to the sinking was the writer Aldous Huxley, who was staying at St Abbs at the time. He wrote to his father saying that:
I dare say Julian told you that we actually saw the Pathfinder explosion – a great white cloud with its foot in sea.
The St. Abbs’ lifeboat came in with the most appalling accounts of the scene. There was not a piece of wood, they said, big enough to float a man—and over acres the sea was covered with fragments—human and otherwise. They brought back a sailor’s cap with half a man’s head inside it. The explosion must have been frightful. It is thought to be a German submarine that did it, or, possibly, a torpedo fired from one of the refitted German trawlers, which cruise all round painted with British port letters and flying the British flag.’
The sinking of Pathfinder by a U-boat made a big impression on Admiral Sir John Jellicoe, who decided to keep his Grand Fleet as far north as the Admiralty would allow. However, other British admirals ignored the threat from submarines to surface ships, leading to disaster later in the month.
Martin-Leake’s brother Arthur became the first man to be awarded a bar to the VC for his courage as an army doctor at Zonnebeke between 29 October and 8 November 1914. He had previously been awarded the VC in the Boer War.
 R. H. Gibson, M. Prendergast, The German Submarine War, 1914-1918. (London: Constable, 1931), p. 6.
<<http://search.proquest.com.connect.nls.uk/hnpscotsman/docview/488299365/7D816E4C02324A85PQ/10?accountid=12801>> Accessed 11 September 2014. Note that this and the next two references are to a password restricted subscription website. I have access to it via the National Library of Scotland.
 <<http://search.proquest.com.connect.nls.uk/hnpscotsman/docview/488297648/7D816E4C02324A85PQ/9?accountid=12801>> Accessed 11 September 2014.
 <<http://search.proquest.com.connect.nls.uk/hnpscotsman/docview/486241221/7D816E4C02324A85PQ/6?accountid=12801>> Accessed 11 September 2014.
 <<http://en.wikipedia.org/wiki/HMS_Pathfinder_(1904)>> Accessed 11 September 2014.