"In the face of the stagnating operations on land, the German high commands exploited the modern weapon of the submarine in a new and daring way. It was Germany’s last attempt to shorten the war and seize a decisive victory."
In the first decade of the twentieth century, the Kaiserliche Marine, led by Admiral Alfred von Tirpitz and influenced by navalist theories, made a commitment to take its fleet to the high seas as a force comparable to that of the Royal Navy. However, in the early days of the Great War, the German navy was still quite inferior to that of the British: compared to the 29 Dreadnoughts of the Royal Navy, totalling 2,205,000 tonnes, the Kaiserliche Marine could provide 17, totalling 1,019,000 tonnes.
Despite its numerical superiority, the British High Command saw the German fleet as a serious threat to its own supremacy. A new strategy was thus adopted. It differed from the Nelsonian tradition of the decisive confrontation, prioritizing the indirect approach of the "fleet always on the alert", deployed as a "large dam" in the Scottish naval base of Scapa Flow. On their part, the Kaiserliche Marine High Command, aware of their fleet’s inferiority and of the impossibility of surprising the enemy, decided to maintain defensive positions, faithful to the principles of the fleet in being. The German strategy was, therefore, to safeguard the fleet as far as possible on the high seas, in the hope that the mine-layers and submarines would undermine the English fleet. All this was in the belief that France’s quick defeat would quickly end the conflict.
There were also geographical reasons behind the German naval passivity. The coastline of the North Sea was deeply indented and protected by islands that defended the bases of Wilhelmshaven, Cuxhaven, and Bremerhaven, not to mention the fact that the Germans could count on the Kiel Canal, an extraordinary "back door" that placed the North Sea in communication with the Baltic and the bulk of the fleet.
These reasons, together with the small size, the difficulty of identifying them, and their ability to perform rapid attacks and then return to naval bases, made submarines the ideal weapon to oppose British power. Thus, during the first months of the war, there were only a few minor clashes and not true naval battles, including a few submarine attacks on the well-defended, fast British battleships, which proved fruitless.
February 1915 saw the turning point that changed the war on the seas. After the failure to win in France, the conflict was looking to be long and demanding; the risk of strangulation of German economic–industrial resources was high. Thus, the Kaiserliche Marine removed all restrictions on submarine warfare; until that moment, they had spared merchant and neutral ships, especially those of the United States. The waters around the British Isles were declared a "war zone" and any ship found in that area would be sunk.
Although the first phase of submarine warfare gave modest results, predicting more profitable developments, it risked provoking United States intervention in the war. The sinking of the ship Lusitania (May 7th, 1915), in which 123 American citizens perished, triggered a diplomatic crisis between the US and Germany that led to the suspension of indiscriminate submarine warfare (September 1st, 1915).
This truce was not destined to last. After the battle of Jutland (May 31st, 1916), the ill-fated attempt by the Hochseeflotte to challenge the British Grand Fleet, the Kaiserliche Marine returned with greater determination and even greater means against the submarine. Initially, the German submarines struck especially in the Mediterranean in order not to hurt American interests. However, in February 1917, Germany once again proclaimed submarine warfare without restrictions. The risk of a US intervention in Europe was considered negligible, because the army High Command believed it was capable of defeating the Allied Forces before the American contingents reached the front.
The pressure exerted by submarines on British supplies was such that in April 1917, 852,000 tons of merchant ships were sunk: 25% of ships did not return. The continuation of a similar situation would have brought the United Kingdom to its knees; however, the German admirals’ promises of a speedy resolution to the war "through strangulation" were far from becoming reality.
Besides rationing and increasing domestic production, the United Kingdom responded by not only placing minefields ever closer to the coast of Germany and by providing aircraft and anti-submersible ships, but also adopting the effective system of naval convoys which inexorably reduced the number of ships scuttled. In June 1917, scuttling was reduced to less than two hundred thousand tonnes, and, before the end of the year, the threat of a blockade was averted. In the early months of 1918, submarine losses were now proportional to the damage caused to the enemy: on May 14th, many of the 125 available submarines were lost.
The reasons for the defeat must be sought within the Kaiserliche Marine. Their intensive use of the submarine was not supported by a sufficient number of trained crews, impairing efficiency and causing men to have nervous breakdowns. Submarines and sailors were present in too low a number compared to the scale of the task assigned to them. The case of the U-35 was indicative of the amount of work to which they were subjected. It was commanded by Lothar von Arnauld de la Perière, and, between March 1915 and March 1918 sank 546,707 tons of allied ships in the North Sea and the Mediterranean, establishing a dramatic record that remained unsurpassed.