Since Germany did not have any overseas bases, naval operations in the North Atlantic required a net of supply ships and tankers (called "Troßschiffe"). Resupply operations with these ships were trained since the mid 1930s and were intensively used during the Spanish Civil War. In Spring of 1939, several Kriegsmarine warships and supply ships - including the battlecruiser Gneisneau - executed a major exercise in the Mid-Atlantic for a operation that would often used in the following two years.
The use of supply ships reached its climax in May of 1941 in conjunction with "Operation Rheinübung" , the one and only operation of the battleship Bismarck . After the loss of the battleship, most of the German supply ships were hunted and sunk by the Royal Navy.
After testing two vessels of an intermediate type, the Germans produced a mature fleet supply ship (trosschiff) - the six-ship Dithmarschen-class. Dithmarschen, a combination oiler and supply vessel, was built by F. Schichau, Danzig, in 1938, for the German Navy. Five were launched between 1937 and 1940; two of them, Altmark (later renamed Uckermark) and Westerwald (later Nordmark), were operational at the start of the war. The sixth unit, Havelland, was launched in 1940 but was never completed.
Besides the use of former civil tankers, a class of specialized supply ships, the Dithmarschen class was build for this task. Although nine ships were ordered, only five were commissioned. They were able to supply warships with fuel, ammunition, supplies and spare parts, in addition they were also equipped with towing equipment to support damaged Kriegsmarine ships. Their payload capacity was 7933 t fuel, 972t ammunition, 790t supplies and 100t spare parts.The Dithmarschens were the longest and fastest tankers then in service withany navy. This length was necessary to achieve high speed. A coincident benefitof their streamlined hull form was exceptional fuel economy; 12,500 miles at fifteen knots, without expending cargo fuel. All this was necessary to support long-range commerce raiding operations that, as was known from the outset, would be furtive, gauntlet-running enterprises.
Two of the five ships survived the war and were used by the British and US navy until the 1950s.