Mar 6, 2015

U-Boot Type XXI in Detail

n Text by Frank Spahr
n Photos by Frank Spahr


In the spring of 1943, Germany was clearly losing the battle of the Atlantic. Improvements in Allied escort material and tactics, combined with cracking the German military code dramatically increased the U-Boats´ losses, rendering them near useless. The German high command saw its best reaction in the speedy development of improved submarines. These were meant to overcome the shortcomings of the current types VII and IX, especially their low speed and little underwater endurance. A future submarine would have to be fast, silent and able to operate submerged for any given time to evade enemy aircraft. 

In the long run, the Germans saw their biggest potential in a propulsion independent from surface air, made possible by the Walter turbine (we aircraft modellers know Mr. Walter for his RATO pods used to bolster the thrust of German aircraft on take-off). It utilised Hydrogen peroxide as fuel; this system would give the boat a hitherto impossible underwater speed of more than 20 knots, yet only limited range.

Two submarine hulls were in the developing stage that would make use of the system. The larger one, the Type XVIII, was designed for long-range operations. It combined a diesel-electric powerplant for long-range duty (getting into the operations area and back) with a Walter turbine (for underwater attack use only). Thus, the hull grew rather large, yet was designed with a streamlined perfection hitherto unknown. The smaller craft, the Type XXII, would be used near the shore and was much smaller.

The project was delayed by the complicated and largely untested power plant: It was felt that it would take several years for it to achieve sufficient reliability for combat use. Moreover, the current production of Hydrogen peroxide was much too small for the projected needs of a large submarine fleet; so adequate capacities would have to be built up beforehand.

The Advent of the Elektroboot
In this situation in the spring of 1943, with dozens of boats lost to Allied forces, as an interim solution it was decided to mate the hulls of the projected Walter boats with conventional powerplants, although with three times the battery capacity than hitherto. This were the types XXI and XXIII which should help turn the tide of the war. Until their deployment, the current types, successively equipped with snorkels, had to soldier on despite staggering losses and somehow bind Allied forces.

The Type XXI was a bigger boat than the Type VII; it was well designed and resembled in no way a stopgap construction. The new boat's hull was designed for high underwater speeds; its shape reflected a change in design: All earlier submarines had essentially been surface vessels that submerged for short spells - this would be a real submarine for the first time. The streamlined shape of the hull and the conning tower produced less noise and made detection by acoustics harder. Moreover, the engines´ efficiency was nearly doubled, giving the Type XXI a top submerged speed of nearly 18 knots for short periods of time.

The vessel's detectability by Sonar or ASDIC could not be altogether eliminated, but in the event it turned out that the new boats were much harder to detect than their predecessors on account of their optimised shape and silent engines. They were also able to sail much faster in silent mode than hitherto.

Six bow torpedo tubes were installed, none at the stern. The boat carried ample spare torpedoes - sufficient for two rechargings in a very short time (20 minutes). Only two twin 20 mm AA guns were mounted in streamlined fairings on the sail, otherwise the boat carried no guns. The sail in its final configuration had only a very small open "bridge", rather hatches only, a total change in design in comparison with the earlier types. It just was not meant to sail on the surface any more. A snorkel system allowed for virtually unlimited operations below the surface, recharging batteries and sailing submerged under diesel power.

An improved passive and active sonar system, called Gruppenhorchgerät and Unterwasser-Ortungsgerät NIBELUNG respectively, enabled detection and attack of enemy shipping without optical contact - another revolutionary feature introduced with the type. Theoretically, the bow-mounted passive sonar would detect enemy shipping and enable the boat to close in near enough for the use of the active sonar. Only a few of its impulses should suffice to compute the distance, speed and bearing of the target with more than sufficient precision for use with the improved LUT-torpedoes. LUT, standing for Lageunabhängiger Torpedo was a new type of guided torpedo to be fired regardless of the target's bearing that would steer an interception course programmed by the torpedo computer. The probability of hits on targets longer than 60 meters was calculated at 95 %.
Crew facilities - though still spartan - were better compared to earlier types. Most crew members had their own bunks (51 for 58 hands); the boat was air-conditioned and equipped with freezers for supplies, thus markedly improving the crew's situation. There were three toilets and a fresh water distiller that increased personal hygiene and crew comfort vastly.

Production and Operations
This design was completed and executed under conditions typical for the second half of the war - the Allied strategic bombing campaign. To evade it, the construction office was housed in a remote location in the Hartz mountains; the boats were built decentralized in modules, which were ferried by barge to a main site only towards the end of construction. Here they were assembled to complete hulls, reducing the period of vulnerability towards air attacks in the shipyard. This system was of course vulnerable, too: Raids on a certain manufacturer could halt progress on all three yards that did the final assembly.

Total construction time compared to former methods was reduced from 22 months to only 9, and that was all that counted in the given situation.

In the end, the overly optimistic schedules weren't met due to the deteriorating war situation and the teething troubles inevitable in such a complex design; but a full 119 Type XXI were completed and delivered in less than a year (28 June 1944 until May 1945).

Only a single Type XXI boat was operationally deployed towards the end of the war. It did not fire a single shot in anger, yet the few encounters made by U 2511 on its raid from Norway between 30 April and 4 May, 1945 showed the Allies´ inability to track the boat with their equipment.

22 Type XXIs were destroyed by the Allies in the yards, 84 were scuttled by their crews following Admiral Doenitz's orders from May 4th, 1945. However, 12 vessels fell into Allied hands intact and gave valuable impulses towards post-war submarine development, both on the eastern and the western side. Major post-war submarine constructions in the Soviet Union, the UK, France and the USA were visibly influenced by the Type XXI.

Enter the Wilhelm Bauer
This particular boat was built as U 2540, launched on 13 January, 1945, commissioned on 24 February, 1945, and scuttled on 4 May 1945. It rested on the bottom of the sea for more than a decade until the German rearmament brought the founding of the German Bundesmarine (Federal Navy) and new submarines were needed.

With the locally defensive tasks given to the Germans within NATO, Germany needed an altogether new and comparatively small type of coastal submarines. These would have to be very heavily armed, hard to detect and as survivable as possible. Quite a number of entirely new subsystems had to be developed and tested for these boats, a huge task to be accomplished at a tight schedule under cold war conditions.

It was felt that training and test bed submarines was needed and that scuttled Kriegsmarine submarines would provide a good solution, especially one more economical in acquisition than other alternatives. So after sifting through Kriegsmarine records, two small Type XXIII submarines for training purposes and later on the large Type XXI U 2540 as test bed were selected. They were salvaged, refitted and used in various configurations by the Bundesmarine. U 2540 was christened "Wilhelm Bauer" after the German engineer who built the first real submarine in 1849, the Brandtaucher. It was commissioned in 1960. The two smaller submarines were called "Hai" and "Hecht" (shark and pike). These three and the large U-freighters of WW 1 ("Deutschland" and "Bremen") are the only German submarines with names instead of numbers I know of.

New subsystems such as engines, snorkel, compressors, mines, anchors, rescue devices, steering systems, torpedoes, acoustic detection devices, a redesigned sail, decoys and much more were tested aboard "Wilhelm Bauer"; later they were operationally deployed in the new types such as 205, 206 and 209. The tests significantly shortened development time and reduced teething troubles.
"Wilhelm Bauer" was turned over to a civilian crew in 1970 and conducted further tests, also participating in manoeuvres as a target ship. But finally, fatigue and damage sustained in several collisions rendered her unsafe, and it was decided to end her career in 1982.

"Wilhelm Bauer" had been very popular with her crews; her ship's arms was a white elephant snorkelling with its trunk - she had been the largest submarine used in post-war Germany. A group of enthusiasts assembled to save her from the scrapper's torch, and the non-profit association Technikmuseum Wilhelm Bauer was founded.

The Walkaround
The boat was decommissioned and rebuilt as far as possible to resemble her wartime appearance. In 1984, she was moored permanently in the museum dock at Bremerhaven next to Germany's Maritime museum and its museum ships. So you have to pay extra to visit her after your visit to this also very interesting museum, but it's worth it and you're supporting the association with your fee.
Of course, the boat is not what it was when built; much has been dismantled and changed when she was converted to a test bed, and some of those latter additions have remained; but you do get a feeling of how it was like living aboard such a vessel.

When we toured the boat, we were inside for about half an hour, with about ten people; I personally would not like living aboard her for weeks together with 58 men, least of all going to war with it. As many times before, it intrigued me to what ends people go to design and build ever more elaborate devices to kill others. My girlfriend's 13-year-old son remarked about the difference between the boat's simplistic and sleek external appearance and the overly complicated interior, with its myriads of valves, levers, switchboxes and pieces of machinery squashed everywhere.

I've toured the very realistic replica of a Type VII boat interior built for the movie Das Boot in Munich, and I've visited the Danish submarine at Aalborg Naval Museum. The Type XXI looked the most spacious of those three to me, yet still more cramped than I would like. Small things roused my imagination: The boxes of lime used to decrease the CO2-content in an emergency, the flashlights mounted everywhere to give the crew light in case of an engine failure. Claustrophobic Scenes from Das Boot rose to my mind, and I was glad to step out into the open.

(Due to the large number the images in this photo essay, the material has been split into parts presented below to facilitate faster downloads - Ed.)