Friday, February 25, 2005
Events of 1917 would prove decisive in ending the war, although their effects would not fully be felt until 1918. The Allied naval blockade of Germany began to have serious impact on morale and productivity on the German home-front. In response, in February 1917, the German General Staff (OHL) were able to convince Chancellor Theobald von Bethmann-Hollweg to declare unrestricted submarine warfare, with the goal of starving Britain out of the war. Tonnage sunk rose above 500,000 tonnes per month from February until July, peaking at 860,000 tonnes in April. After July, the newly introduced convoy system was extremely effective in neutralising the U-boat threat. Britain was safe from the threat of starvation. Even more importantly, April 1917 finally saw the formal entry of the United States into the war, in response to the U-boat attacks.
Indicator Nets were predominantly deployed by the British Royal Navy as a means—albeit generally unsuccessful—of discouraging enemy (usually German) submarines from entering Allied waters. Constructed using light steel nets these were anchored at various depths to the sea bed around key Allied naval bases and were intended to entangle enemy U-boat traffic, although even then submarines were often able to disentangle themselves and escape before they were blown up by depth charges. They were seldom used as the sole anti-submarine measure but were instead mixed with other defences, which usually included extensive minefields and patrolling warships. In time mines were actually attached to the nets, thereby reducing the survival chances of an entangled submarine.
Once a submarine became entangled a marker buoy attached to the net would drift along the surface indicating enemy activity below. The first example of indicator nets assisting in the destruction of a German U-boat occurred at Dover when the U-8 became entangled on 4 March 1915.
Indicator Nets were used extensively—dropped from light fishing craft—at both Dover and Otranto Barrages. Individual nets were sometimes as much as 100 metres in length. While these were ultimately of some benefit at Dover (where the barrage was constantly fine-tuned to produce results) they proved ineffective at Otranto, with gaps between the light steel nets sufficiently wide to allow enemy submarines through. Under cover of darkness U-boats could also thwart the nets by coasting along the surface, as happened at the Otranto Barrage.