1917 - année de la guerre sous-marine à outrance
On the 9th January 1917, Kaiser Wilhelm II imposed a maritime blockade on Europe: "I am giving the command for unrestricted submarine warfare to begin in earnest on the 1st February ". Wanting to economically suffocate the Entente, he authorised his fleet to attack vessels flying neutral flags, which had already been persuaded to trade in favour of the Entente. Germany thus ran the risk of confrontation with the United States, the only great power still at peace, but she was relying on winning through her skilful control of a new weapon: the "U- Boot").
1914-1916: limited submarine warfare In the early years of the war, control of the sea was left to the "dreadnoughts", modern battleships that were both powerful and fast. Submersibles were first used as coast guard ships, particularly in front of the naval shipyards. At the start of hostilities, the British deployed their own in the North Sea, where they contributed to the maritime blockade of Germany. "U-boots" also patrolled in the Channel and the North Sea, searching for the Entente's war ships in the hope of restabilising the forces present. For the first time torpedoes were to demonstrate their effectiveness against warships which, in 1914, had not taken any special precautions against this invisible enemy. However, the only consequence of these successes was to warn the Navy of this new danger. In the end, we believe that the German submarines missed their best opportunity of surprise in neglecting to take out the ships transporting the British Expeditionary Corps to France. At the beginning of 1915, when it was established that the war was to be neither short nor easy, the economy and the morale on the home front became issues that were just as important as the military fronts. Then, following the battle of Dogger Bank, the German high seas fleet, the pride of the Empire, received orders from the Kaiser to take no further part in combat. For Admiral Tirpitz, a submarine war on trade became the only course of action open to him.
On the 4th February 1915, Germany declared the British waters a war zone and ordered the destruction of all ships found there. The tragic consequences of this order are well known: on the 7th May, U-20 torpedoed the Lusitania without warning, with the loss of 1198 lives. On the 19th August, another steamship, the Arabia, was sunk. These events gave rise to great indignation in the United States and an official protest from President Wilson. On the 18th September, Germany ended her attacks. In 1916 her ships remained in port or were sent on limited missions. There was however the reported crossing of two unarmed "cargo submarines" between Baltimore and Bremen, returning loaded with precious materials for the war economy: an adventurous attempt to break the blockade of the Entente. In any case, the effectiveness of this first campaign was limited by the low number of submarines available: never more than 25, or a quarter in operation at any one time. German commanders came to the conclusion that in order to be completely effective, their submarines had to be involved in great numbers and without any restriction on their choice of targets. It was through terror that they would prevent free movement by sea.
1917: opting for all-out war Why did the Kaiser risk taking a course of action that he had rejected in 1915-1916? In fact, he left it to the imperial chief of staff who planned for the year ahead to abandon the costly campaigns on the Western Front and corner Great Britain into surrendering by cutting off supplies, even at the cost of war with the United States. It was the first time that Germany had entrusted the leading role in operations to the navy. The German submarine fleet had become considerably stronger from 1915. It numbered 128 submarines, deployed across all the seas in Europe: 26 in the Adriatic, 3 in the Black Sea, 2 in the Baltic and 97 in German and Flemish bases. These "U-boot" were formidable vessels, reliable and hard wearing, without equal in any other navy. The ocean-going model had a capacity of 850 to 1,000 tonnes, with a surface speed of 16 knots and dive speed of 8 and a range of 7,000 nautical miles. Some submarine cruisers were even designed to reach the American coast. Other classes of vessel were invented for specific missions, such as the defence of the coast (UB) or mine laying (UC). Submariners were hailed as an elite body with their own heroes, such as Wenningen and Arnault de la Perrière. To bring Britain to its knees, they would have had to sink 800,000 tonnes per month and the early stages of the war without restrictions came close to keeping this promise with 540,000 tonnes in February and 593,000 tonnes in March. The cost of maritime transport doubled and tripled. April was the high point of the crisis: 881,000 tonnes. Neutral navies yielded and Germany believed she could triumph. All she had to do was keep up this devastating rate, but from the following month onwards the curve of losses fell off, becoming less than 400,000 tonnes after the month of August. From then on the commercial war was lost for Germany, as summed up by Lloyd George in 1918: "We are sinking more submarines than the Germans can build; we are building more warships than the Germans can sink. The submarine war is still a threat but is no longer a danger. We have warded off the most serious hazard that we could have faced".
The United States' entry into the war on the 6th April 1917 was a major consequence of these events, but it is not the only reason that the situation was turned around. The naval construction programme immediately launched by President Wilson could not yet bear fruit. The reasons were rather the rapid exhaustion of the German fleet and the defensive measures taken by France and Great Britain. In England, an anti-submarine committee had at its disposal a fleet of trawlers, yachts and large craft for
surveillance along the coasts and to protect fishing boats, whilst in France fishing fleets were armed. But the fleets of the two countries lacked the warships required for the security of the great maritime routes. In 1917 it was necessary to protect 10,000 merchant ships sailing in isolation. Camouflage, sailing in a zigzag fashion and other passive protective measures were not enough. The only solution was to organise escorted convoys, as requested by France. Britain, hitherto against this on the grounds of the freedom of navigation for ship owners and in order to save the time that would be lost forming convoys, was forced to agree in the face of the intolerable losses in the early months. The decision was their salvation: just 0.2% of convoy ships were lost, compared to 7% of those sailing unescorted. At the same time the emphasis was placed on improving the means for anti-submarine warfare, by increasing the weight of grenades and adopting microphone listening apparatus, the forerunner of sonar. Another innovation - the naval air force -was being developed, totalling 1,000 aircraft in France at the end of the war. These deterrents made the task of the "U-boot" more difficult, as they in turn became targets and had to make do with attacking when diving: 65 of them were scuppered that year. On the sea too, the offensive turned into a war of attrition. The increased losses and fatigue amongst the crews can explain the ultimate defeat of the German fleet which, despite a satisfactory annual balance sheet -11,000,000 tonnes of ships sunk, including 6,100,000 belonging to the Entente - did not have the material means of maintaining the pace in the face of the Americans' 30,000,000 tonnes.