Following the defeat in World War I the terms of the Versailles Treaty of 28 June 1919 shrank the former Imperial German Navy with some 80.000 soldiers to a new Reichsmarine with a mere 15.000 soldiers and a few warships (6 armoured cruisers, 6 light cruisers and 12 torpedoboats), submarines were deleted from the new Navy´s inventory entirely. (see Remark)
After 1933, the National-Socialistic Germany embarked on a huge rearmament programme. On 18 June 1935 agreement was reached with Britain, allowing Germany to build up a Kriegsmarine (the name “Kriegsmarine” was officially introduced on 01 June 1935) of up to 35 % in size of the above water tonnage of the Royal Navy and 45 % of the numbers of the Royal Navy´s submarine force. In the following years international restrictions (including the Washington Naval Treaty) were gradually disregarded, until in 1939 a new Fleet Construction Programme for a comprehensive and versatile Navy was developed, which comprised the construction of aircraft carriers, battleships, a great number of cruisers and light forces, inter alia some 249 U-boats, to be completed by 1947/48. Therefore, at the outbreak of World War II the Kriegsmarine was still very much in build up and the Commander-in-Chief of the Navy, Grand Admiral Erich Raeder, directed to concentrate naval shipbuilding in compliance with the Fleet Construction Programme with selected types and numbers of vessels only. Naval personal had increased from former 15.000 soldiers to more than 78.000. When Britain declared war on Germany, Raeder recognized that the Kriegsmarine would be no match for the seapower Britain in terms of armament. As an example: At this moment of time, there were just 26 U-boats available for oceangoing warfare. He assessed the rate of success of the war at sea just against Britain alone rather pessimistic, he even wrote in his diary that now his surface units could only “die in decency” and his U-boats would never “decide the war at sea”.
The imbalance of the Kriegsmarine´s armament with far too much weight on surface forces in contrast to the low number of U-boats should fully prove its disadvantages as Britain´s dependence on safe supply routes across the Atlantic Ocean was such a crucial factor. Although there were a few spectacular actions by surfaces forces of the Kriegsmarine it were, above all, the U-boats which inflicted appreciable losses to the Allies´ Naval forces and their supply shipping across the sea. The Kriegsmarine was able to support key strategic missions of the Wehrmacht (German Armed Forces) only by all out efforts, such as the occupation of Norway, plans for the invasion of Britain had to be abandoned all together and in the Mediterranean sustained sea power or at least such power over restricted areas was never achieved. The armament programme was changed to foster a faster construction rate of U-boats and generated soon a quick growth of the U-boat force – after 68 U-boats in 1940 as many as 129 U-boats were built in 1941, and in 1942 with 282 U-boats built the highest ever number of all annual new constructions was reached.
The number of losses discounted from the above figures the number of U-boats available at any time grew significantly: in 1941 there were already more than a 100 U-boats, in 1942 that number went up to more than 250 and in 1943 the number of 400 was passed, a figure that could be kept until the end of war. With that there were periods were more than 60 U-boats could operate executing combat missions in allocated sea areas simultaneously. Still, despite many remarkable successes during the first years of war a break down of the Allied sea lines of supply between North America and Britain could not be achieved.
The Battle of the Atlantic was lost in Spring 1943, as the anti submarine capabilities of the allies became too effective and the construction programme for merchant vessels was in full swing, enabling to compensate losses in ship cargo capacities without major problems, while at the same time the losses of U-boats reached a scale that was hardly to be justified any longer. The ongoing employment in coastal warfare by minesweepers and fast patrol boats exempted, there were hardly any missions by surface forces any longer from 1943 to 1945, it were the brave U-boat crews that bore the efforts of the war at sea further, despite terrible losses. In 1943 some 237 U-boats were lost, in 1944 another 241 and during the last months of 1945 again 153 units.
At the peak of war the Kriegsmarine had a size in personnel of about 750.000. The quota of the U-boat force was not greater than 5 % of that and only about 41.000 Naval personnel ever served with the U-boats, although in the end that force carried the burden of the war at sea.
The German U-boat force fought under heavy own losses – no other branch of the Wehrmacht (German Armed Forces) had to take almost 70 % own losses – and it inflicted more damage and losses to the allies at sea than any other branch of the Kriegsmarine. Therefore, the character of the Kriegsmarine soon changed to being an U-boat Navy, the enormous armament programme of more than 1.100 U-boats built and commissioned during the war might clearly underline this. Undoubtedly, the U-boats were an enemy much feared by the Allies (Churchill:”…The U-boat war was our worst evil…”), they were, however, in no phase of the war at sea “decisive” (as Grandadmiral Raeder predicted it in 1939) for the outcome of the war.
Hence, the U-boats had never pushed the Allies to the brink of defeat, too mighty was the ability of the sea power Britain and, from 1941 onwards, the USA to compensate losses in shipping capabilities and to execute a more and more efficient anti submarine warfare.
During World War II German U-boats sunk about 2.800 merchant vessels with a total of 14,3 Million tons and another 150 warships. With that they had a share of about 69% of the sinkings (some 21 Million tons) by the Kriegsmarine, the share of the surface forces was a mere 7 %. At the same time the US and Britain managed to build some 39,5 Million tons of shipping space at their shipyards.
At the end of the war the Kriegsmarine did demonstrate another time its ability to tackle huge tasks with all its might, including using U-boats, when during the last months of the war about 2 Million refugees and soldiers were either transported from the Eastern German provinces to the West across the Baltic Sea by Naval vessels or the merchant transport vessels used for that were escorted.
Losses of the Submarine Force in WW II: 28.756 officers, petty officers and ratings – six times as many as in WW I. The names of all those, whose grave is the sea, are shown on metallic rolls of honour at the U-boat Memorial at Kiel-Möltenort.