'Nordmark' was a German naval operation against Allied shipping in the North Sea (18/25 February 1940).
Under the command of Admiral Wilhelm Marschall, the Flottenchef, a force comprising the battle-cruisers Scharnhorst and Gneisenau, supported by the heavy cruiser Admiral Hipper and destroyers Karl Galster and Wilhelm Heidkamp (Wolfgang Zenker having been compelled to turn back as a result of ice damage) managed to extricate themselves from their bases in the icebound river estuaries of northern Germany with the intention of attacking, in the area between Norway and the Shetland islands group, British convoys plying the route between the UK and Norway. Air reconnaissance had warned the British of the German ships' departure, and the only convoy in the area was recalled as a cordon of submarines was disposed to intercept the German ships' likely route and as the main units of Admiral Sir Charles Forbes’s Home Fleet were moved into the area from the Clyde.
'Nordmark' was hampered by lack of air reconnaissance and lack of targets, and returned empty-handed. Icebreakers had to be used to clear the estuaries of the Jade and Weser rivers before the German ships could re-enter Wilhelmshaven.
At the same time the destroyers Paul Jacobi, Theodor Riedel, Hermann Schoemann and Leberecht Maass of Fregattenkapitän Rudolf von Pufendorf’s 2nd Zerstörer-Flottille, preceded by the torpedo boats Luchs and Seeadler, had escorted the larger warships through the Skaggerak before being detached to search independently for Allied mercantile traffic.
Other support for 'Nordmark' was provided by U-boats, of which three were to operate between the Shetland islands group and Norway, two in the Fair Isle Channel, and three off the Pentland Firth; three other boats were held in reserve near the north coast of Scotland. The boats deployed were U-13, U-18, U-19, U-22, U-23, U-57, U-60, U-61, U-62 and U-63,, as well as U-14 off Kinnaird Head.
Of these, Oberleutnant Wolfgang Lüth’s U-9 sank the 1,213-ton Estonian Linda, Oberleutnant Herbert Wohlfarth’s U-14 the 1,066-ton Danish Sleipner, 1,646-ton Swedish Liana, 1,526-ton Swedish Osmed and 1,064-ton Danish Rhone, Oberleutnant Jürgen Oesten’s U-61 the 1,406-ton Panamanian El Sonador and 4,297-ton Norwegian Sangstad, and Oberleutnant Günther Lorentz’s U-63 the 3,840-ton Swedish Santos. Kapitänleutnant Claus Korth’s U-57 sank the 10,191-ton British Gretafield and damaged the 4,966-ton British Loch Maddy, whose destruction was completed by Kapitänleutnant Otto Kretschmer’s U-23, which also sank the destroyer Daring, part of the HN.12 convoy’s escort. Oberleutnant Joachim Preuss’s U-10 sank the 1,819-ton Norwegian Kvernaas and 4,537-ton Dutch Ameland in the southern part of the North Sea.