The Germans were happiest in the construction of sailors, where, better than elsewhere, they were able to maintain a certain continuity of their studies after 1918, and this is probably the explanation of the fact that the U-boats were the most successful units of all the types of ships of the German Navy.
It was only in the field of submarines that the German Navy of 19141918 managed to count a higher number of units than that of the Royal Navy. The German submarine fleet had on its side the number but also the diversity of types:on the one hand, the medium tonnage submarines which it continued to build and improve during the war, and, on the other hand , the large submarine cruisers armed with 140 mm guns and capable of crossing the Atlantic, the small U.C. class minelayers and, finally, the U-Boote type coastal units, small submarines at first, but which were to evolve into a larger formula, which would be the basis of the U-boat plans of World War II. At the end of the First World War, Germany lost all of its submarines, but the teams that had designed them were kept working abroad, in Finland, Spain, Holland and Sweden. The Germans had to wait until 1934 before being allowed to own submarines, but their specialists had ready improved versions of units built outside Germany for the foreign navies, versions extrapolated directly from the best achievements of 1914-1918. br class='autobr' /> 
The U-boats performed remarkably early in the hostilities, although 'they were handicapped by the malfunction of their torpedoes, which were too complicated and insufficiently developed. During the period from 1941 to 1943, the weaknesses of the torpedoes having been overcome and a sufficient number of units built, the submarines came very close to prevailing. However, as the months passed, the skyrocketing tonnage manufactured by the Allied shipyards began to bear fruit and, even better, the Allies began to win the scientific battle. New radar types appeared, forward weapons like the "Hedgehog" and "Squid" made Escort attacks more deadly, while Acoustic Seeker Rockets and Torpedoes enhanced, for example, elsewhere, the means of the planes.One of the most effective actions against the U-boats was the use that the Allied ships made of the radio links of the German submarines with their bases to locate them. escort planes and air cover is exposed below. false echoes on the ASDIC), radar detectors or additional 20 mm heavy machine guns transforming the submarines on the surface into anti-aircraft traps against the Allied planes. Despite everything, the U-Boats were dominated and definitively defeated at the end of the war. end of 194 3 in their main theater of operations, the North Atlantic. On the German side, the number of trained commanders and crews declined, while the experience and skill of the Allies increased. In the final days of the war, the Germans were about to launch a counter-offensive using entirely new submarine designs, but it was far too late. Before that, the snorkel had been put into service; it gave submarines a much greater range when diving, but it was only a mainly defensive novelty.
The first submarines built for the “Kriegsmarine” were of the oceanic type I, on the basis of the plans of two units manufactured in Spain for Turkey, and of the type II. The latter were small vessels used mainly for training.
The largest number of submarines built by Germany during the war must have been of the Type VII. This model was
developed by means of a Finnish submarine, from the last U-boats of the 1914-1918 war. The Type VII submarines had the smallest displacement that could be suitable for ocean navigation, they were equipped with good armament and behaved well in diving; the VII B variant of this type had some improvements over the original type VII A. The VII Bs were a little larger, had better sea-keeping and their diesels were more powerful. The VII Cs that followed carried more reserve torpedoes and received better anti-aircraft defenses. This model became the standard type in production and was built in greater numbers than any other; also, at the end of the war, the VII C had to deplore the record number of units sunk, in any place that it was. At the same time, they established a similar record for the number of merchant ships sunk, not to mention a good number of warships.
During the conflict, under construction or repairs, these submarines received various modifications; first of all, they were fitted with a greater number of 20 and 37 mm guns, which generally led to the disembarkation of the 88 mm gun. Some U-boats called "D.C.A. Traps" were equipped with an impressive number of automatic cannons in order to discourage attacks from Allied anti-submarine planes, with an increasingly large range of action. The facts took care of demonstrating that this was not a good solution.
Snorkeling was more successful, but it did not appear until the end of the war to give a little respite submersibles that survived the battle of the convoys. The last models of the type VII had more resistant thick hulls in order to increase their maximum immersion yet already very high, much greater than that of the submarines of other nations. Type VII D was a minelayer, a variant with an additional hull section on the rear of the kiosk, equipped with vertical minelaying tubes. The various designs of the Type VII had been very successful boats in their time, but they had become obsolete towards the end of the war and easily destroyed.
The Type IX A, larger than the type VII, carried a large number of reserve torpedoes for its six tubes (22 in total) or, in their place, a load of mines. The type IX B was similar to the IX A but it had larger holds, hence an increased radius of action, and the following model, type IX C, was further improved in this respect. Larger and heavier, these boats did not have the rating of their crews as much as the VII types and yet it is to a submarine of this type that the record for the tonnage of merchant ships goes.
The first two units of the type IX D were special cargo submarines
designed for links with Japan and capable of transporting small quantities of products of vital importance. The second model of IX D was also intended to intervene in distant theaters of operations, but it was armed with torpedoes or, if necessary, mines.
A series of large minelayers of the type B was armed only with two aft torpedo tubes and a defensive artillery, apart from the sixty-six mines contained in interior and exterior vertical tubes. They were more often used as submarine refuellers than as minelayers.
The importance of the role of "cash cow" submarines became greater and greater as the successes of the Allies in the North Atlantic forced the U-boats to search further and further away for areas where hunting was easier, a quest which proved to be illusory. A special type of submarine tanker, the XIV, was designed and built for this purpose; shorter and more pot-bellied than the IX D, its displacement was comparable. These submarines were relatively easy targets to hit and, with good intelligence, many of them were detected and sunk, especially by US escort carriers operating in the South Atlantic.
Towards the end of the war, Germany made giant strides in submarine design and built new units that
were real submarines capable of operating almost all the time while submerged, instead of behaving like submersibles designed primarily for surface actions interrupted by brief dives. This result was obtained by designing the hull for high diving speeds, installing powerful storage batteries for the same purpose and snorkels to recharge these batteries. The largest version of this type is the XXI, and the coast defense version is the smaller Type XXIII.
U 47 (Type VIIB)
Surface movement , 753 t;
diving .857 t
Length 66.51 m at the waterline
Width 6.17 m
Draught 1.67 m
Surface propulsion , 2 lines of trees, diesel-electric, 2,910 hp, 17.25 knots; diving , 2 shaft lines, electric, 750 hp, 8 knots.
Artillery :1 cannon of 88 mm; 1 x 20 mm AA machine gun
L.T Tubes . 5 × 533 mm torpedo tubes
Launched on October 29, 1938 at the Germania shipyards, in Kiel
U 64 (Type IXB)
Surface movement , 1068 t;
diving 1197 t
Length 76.50 m
Width 6.76 m
Draft 4.70 m
Surface propulsion 2 rows of trees, diesel 4,400 hp; 18.25 knots;
diving electric motors, 1,000 hp, 7.25 knots
Artillery :1 cannon of 105 mm; 1 x 37mm AA machine gun; 1 or more 20 mm AA machine guns.
L.T Tubes . 6 x 533mm torpedo tubes, four forward, two aft
Launched September 20, 1939 at the A.G. Weser shipyards in Bremen