SM U-12 was a German submarine, built in 1911 and sunk off Scotland in 1915. It was the first submarine to launch a plane at sea. U-12 was a Type U 9 U-boat built for the Imperial German Navy. Her construction was ordered on 15 July 1908 and her keel was laid down by Kaiserliche Werft in Danzig. She was launched on 6 May 1910 and commissioned on 13 August 1911.
The German Empire was the first nation to experiment with submarine aircraft carriers. Oberleutnant zur See Friedrich von Arnauld de la Perière of the Naval Air Service and U-12s commander, Kapitanleutnant Walther Forstmann, theorised that they could increase the range of their seaplanes by carrying the aircraft out to sea on the deck of submarine and launching the seaplanes after the sub partially submerged, allowing the plane to float off.
At the star of World War I, U-12 formed part of I submarine Flotilla. Forstmann commanded the boat for the first year of the war. U-12 torpedoed the British gunboat off of Deal on 11 November 1914. This was the first Allied casualty from submarines based in Belgian ports.
On 6 January 1915 U-12 left Zeebrugge transporting a Friedrichshafen FF.29 seaplane on its deck. Once beyond the safety of the breakwater, Forstmann realised that the heavy swell might swamp the aircraft and ordered the immediate launch of the seaplane. He flooded the forward tanks and Arnauld floated the seaplane off the deck and took off from the sea. The plane flew along the English coastline undetected and returned safely to Zeebrugge.
In February 1915 command of U-12 passed to Kapitänleutnant Hans Kratzsch, with Forstmann moving to take over command of the newly commissioned . The boat sank the British steamer Aberdon on 9 March off of St Abb's Head. The following day U-12 was hunted down by three Royal Navy destroyers, , , and .
The submarine attempted to dive, but was rammed by Ariel before being shelled by Acheron and Attack. It sank with the loss of 19 lives, although 10 survivors were rescued.
In January 2008, divers Jim MacLeod, of Bo'ness, and Martin Sinclair, from Falkirk, found the wreckage of U-12 about 25 miles from Eyemouth after a five-year search.
U-12 sank two ships during its career.