Flanders U-boat flotillas

The Flanders U-boat flotillas were Imperial German Navy formations set up to prosecute the U-boat campaign against Allied shipping in the Channel and the North Sea (British Home Waters) during the First World War. Originally operating as a flotilla, it was split in two during the latter part of the war.

U-Boat Flotilla, Flanders
Active	Raised March 1915, dissolved October 1918
Country	Germany
Branch	Imperial German Navy
Type	U-boat flotilla
Base	Bruges, Belgium
Nickname(s)	Flanders flotilla

On 18 August 1914, ten days after the start of World War I, the German Navy started to explore the idea of small, coastal submarines which could be built in a matter of a few months. On 11 September the idea was rejected but on 25 August as the German Army made rapid advances in Belgium and reached the coastline, the idea was put on the table again and the German Navy asked naval yards for design for a small U-boat which could be transported by rail. On 15 October fifteen Type UB I U-boats were ordered, with construction time of four months only. The U-boats were transported in three parts to Hoboken, where they were assembled and subsequently transported on pontoons to the port of Bruges in occupied Belgium.^[1] Based on the same Type UB I, the German Navy ordered on 23 November a further fifteen Type UC I coastal minelaying U-boats, of which eleven were transported in sections to Flanders.^[2]

The Flanders flotilla was constituted in March 1915 in Bruges. Commanded by Kapitänleutnant Karl Bartenbach, the force comprised nine Type UB I U-boats at the end of April 1915.^[3][4] The boats used Zeebrugge and Ostend as exit ports; UC minelayers joined in late 1915.^[5] Throughout the campaign the Flotilla grew, though losses also remained high, as the unit bore a considerable proportion of the trade war (Handelskrieg) around the British coast. During 1916 12 boats were lost;^[6] in 1917 this rose to 29 boats, 9 UB- and 20 UC-type.^[7]

In October 1917 the force was split into two full flotillas and Bartenbach, now a Korvettenkapitan, was made flotilla leader (Führer der U-boote, FdU).^[7] The 1st Flanders Flotilla, under K/L Walther, comprised 8 UB- and 12 UC- boats at its formation. during the next twelve months 10 UB- and 5 UC- boats were lost. With replacements the unit strength in 1918 was 16 UB- and 9 UC- boats.^[8] The 2nd Flanders Flotilla, led by K/L Rohrbeck, comprised 12 UB- and 12 UC- boats; 12 UB- and 4 UC- boats were lost but with replacements its strength in 1918 was 17 UB- and 7 UC- boats.^[8] Towards the end of 1918 the base at Bruges was abandoned as the German armies on the Western Front retreated. The surviving boats of the flotillas were surrendered at Harwich in November 1918.