The Electroboats

The Origins and Development of The Wonder U-boat

                               
                                       Type XXI Elektro boats after the surrender.

In the very last moments of the Second World War new U-boats, based on a completely new concept, saw action. Had they arrived earlier, they might have changed the outcome of the Battle of the Atlantic and more. The concept itself inspired the submarine design for the next two decades. Even more, the hull design of one of the Electroboats was adopted and used in the development of the world first nuclear submarine.

1. Origins

The development of the German U-boat fleet in 1935-39 was based entirely on the First World War principles. However, it had already been known that England was in possession of the underwater location device ASDIC(Anti Submarine Detection Investigate Comitee) which was to counter the submarine threat. Not surprisingly, the Second World War started with great speculations about the effectiveness of the U-boats.
Soon it had become apparent, that ASDIC was not so effective as claimed and certainly it was of no use against a surfaced U-boat. And it was a surfaced group attack at night, known as Rudeltaktik, that proved itself so lethal to convoys. Without a surface location device the escorts were not able to see a narrow silhouette of the surfaced U-boat at night or in bad weather. The same applied to aircraft.
The U-boat training programme was adopted to the principle of Rudeltaktik. The emphasis was on the skills of the commander and crew as it was believed that the experience was the main decisive factor in the battle.
The technical development was somewhat left behind. Doenitz got acquainted with Professor Walter and was quite impressed with the idea of a closed circle engine. Such an engine required no air intake and therefore could run when a submarine was submerged and at the same offered enough power to achieve speed around 25 knots. The idea was further developed and in 1940 the prototype V80 indeed travelled submerged at the speed of 26 knots! Therefore, the concept was regarded as the right answer for the need of high underwater speed. The amount of technical difficulties made it clear that it would take a long time to convert the prototype into an ocean-going attack U-boat. At that time, however, no one seemed to be worried as the conventional U-boats still enjoyed a high rate of success when operating on the surface at night.
However, there were early warnings that this situation might change dramatically. On the pitch black night 30th November - 1st December 1941 while attempting to penetrate the Straits of Gibraltar, U-96 was accurately located and bombed by the radar-equipped Sqdn. 812 Swordfish. Her commander, Heinrich Lehmann-Willenbrock, insisted that the aircraft must have been using a new location device. In spite of the fact this statement was made by one of the most experienced U-boat commanders, no one believed it was the case. In particular, no one believed an accurate radar set can be so small, it could fit in an aircraft.
Another warning came also in December 1941. It was the convoy battle around HG-76. The convoy was protected by an aggressive support group including an aircraft carrier,  lead by an ASW expert, Capt. Walker. Although a total of 14 U-boats were assembled in the area, only 5 ships were sunk at a cost of 4 U-boats directly involved in the operation (U-131, U-434, U-574 and U-567). A shocking exchange rate which later became normal. In fact a few more were sunk in the area at the same time. U-567 was commanded by Engelbert Endrass, an experienced Knight Cross Holder, while other boats by relatively inexperienced commanders. BdU was convinced that the success was entirely depending on the experience of attacking U-boats. This is why when Doenitz was sending Endrass, in whom he had great confidence, he had also signalled: "Hold on to that convoy. I'm sending Endrass". In vain.
There were a few more warnings. It was clearly demonstrated that with the arrival of the radar-equipped aircraft and escorts, especially when put together in a support group with a carrier, the conventional U-boats may achieve nothing but heavy losses. Unfortunately for the Germans, these warnings were not taken into consideration serious enough to affect the development plans for new U-boats, their weapons and electronic equipment. It was almost a year later, when the loses in the North Atlantic convoy battles became alarmingly high, when something finally happened.
November 1942 was the best month in the in terms of tonnage sunk during the U-boat War. The majority of sinkings happened along the North Atlantic convoy routes, in the so-called Atlantic Gap, out of the reach of land-based Allied aircraft. U-boats returned to the North Atlantic in the second half of 1942, when gradually stronger US anti-submarine forces made operations in the Western Atlantic and the Caribbean impossible. However, the British had enough time to increase the number of escorts, aircraft and develop new techniques. The Germans also increased the number of U-boats and in the second half of 1942 on average a hundred were at sea every day. All these factors inevitably lead to fierce convoy battles of previously unknown proportions.

2. Development

The scope of the November 1942 meeting was to examine the progress of the Walter U-boat which was the only possible solution to the situation that developed in the North Atlantic. Although the Walter concept and the first prototype V80 initially demonstrated remarkable performance, it had also delivered a whole range of new technical problems. These were particularly related to fuel required by the closed circle Walter engine - highly flammable Perhydrol. Due to the high rate of Perhydrol consumption a combat Walter U-boat would require a massive fuel tank, otherwise the underwater performance would not be satisfactory. The existing hull designs could not offer adequate fuel bunkerage. Therefore, Professor Walter presented a new double-hull design, forming a figure 8 in section. The upper part accommodated the crew, engines and torpedoes. The lower part used entirely as a fuel tank. The design was later known as Type XVIII.
However, it became clear that in spite of the advanced planning, the new Walter U-boat was not going to be operational in any foreseeable future. Moreover, any prospect on the Walter project would require a diversion of the shipyard resources from Type VII and IX building, which was at that time out of question. Therefore, it was decided to carry on the Walter projects but still on a limited research scale.
The meeting would end up in disappointment if it was not 2 engineers, Schuerer and Broecking, who realized a very simple solution, utilizing the new Walter hull design. Instead of using the lower section for Perhydrol, the idea was to install additional batteries there. This would effectively triple the battery capacity of the boat. Initial calculations showed that the performance of the new concept is far better than of the conventional U-boat, although not as good as of the Walter one. This however fully satisfied Doenitz and the development went ahead. The only problem was that the displacement of the boat was around 1600 tons - and at that time smaller boats around 1000 tons were preferred as much easier too handle and more resistant to depth-charges.
By the end of January 1943 detailed theoretical calculations were finished and by the end of June 1943 a preliminary design was completed. The following are the the most important features of the Type XXI design:

• Displacement of 1620 tons
• Streamlined hull with 6 forward torpedo tubes
• Full submerged speed of 18 knots for 1.5 hours
• Submerged speed of 12-14 knots for 10 hours
• Silent submerged speed of 5 knots for 60 hours
• Water-pressure controlled depth keeping equipment
• Semi-automatic hydrolic torpedo reload system
• New improved underwater listening device
• Sonar
• Radar-search receivers (to detect enemy radar)
• Radar
• Deep freezer
• No deck gun
• No external torpedo storage containers
• Schnorkel

The Type XXI design was presented to Hitler at a conference on the 8th July 1943 in order to obtain his approval for additional demands on the industry. The approval was given and on 13th August 1943 an order was given for the transition to building Electroboats. At the same time the building programme of the conventional boats was to be carried on, in order to make up for the expected losses till the arrival of new boats. The development of Walter boat was to continue, and in addition to 4 prototypes being built and order for additional 24 Type XVIIB and 2 Type XVIII boats was given.
Together with the development of Type XXI work had started on a small Electroboat for coastal operation. The large Electroboat was initially supposed to replace Type IX boats but after the May 1943 disaster it was obvious that it should also replace Type VII convoy attack boat. However, because of the size, Type XXI boat was not suitable for shallow water operations, particularly the North Sea, Black Sea and the Mediterranean. Therefore, a small Electroboat was proposed with the following features:

• displacement of 234 tons
• streamlined hull with 2 forward torpedo tubes (torpedoes in the tubes, no reloads)
• full submerged speed of 12 knots
• new improved underwater listening device
• easy to control
• Schnorkel

The plans for the small Electroboat, Type XXIII, were presented together with Type XXI and got approved.
Author could not positively established wether the Schnorkel was the inherent part of the Electroboat design from the very beginning or was added later, after experience was gained from the heavy losses in the first part of 1943. Certainly, Schnorkel was studied and added to the Walter U-boat concept at about that time. However, whenever the Schnorkel was considered, the final design of both Electroboats were equipped with the most modern telescopic device and were able to use it at much greater speeds than conventional Schnorkel U-boats.
A detailed production plan was worked out between July and December 1943.
At least 18 months were required to build a Type XXI U-boat under a conventional construction procedure (with boats built from start to finish on a single slip). This effectively meant that prototypes would be ready only in November 1944 and regular production boats would be ready for operational use in 1946. This was not acceptable.
Therefore the Minister for Armaments, Albert Speer, decided to consult the matter with Otto Merker, with experience in the mass production gained in the car industry. Eventually, an alternative production method was proposed with the following assumption:

• no prototypes
• pre-fabricated sections manufactured in parallel, in distributed works around the country
• sections to be transported to the shipyard by water (big Type XXI sections) or rail (smaller Type XXIII sections)
• final assembly of sections at the shipyard

The detailed building plan for the Type XXI consisted of the following stages:

acquisition of raw materials and transport to steel works	16 days
steel work	40 days
transport to the section building plant	5 days
section building	50 days
transport to the yard	4 days
assembly at the yard	50 days
final work after launching	6 days
total building time per boat	171 days (6 months)

The method eliminated the bottleneck caused by the limited shipyard resources. Instead of occupying a slip for the entire building process (18 months mentioned) it was required only for approximately 80 days of final completion (as it turned out to be). Hence the shipyard building effectiveness was multiplied by almost 7.
The following are the detailed descriptions of Type XXI and XXIII sections.

Type XXI section description

Section	description	weight (tons)	length (meters)
1	Stern with stern compartment	65	12.7
2	Electric motor room	130	10
3	Diesel engine room	140	8.4
4	Aft living quarters	70	5.3
5	Control room and galley	140	7.6
6	Forward living quarters	165	12
7	Torpedo stowage room	92	6.8
8	Bows with torpedo tubes	110	14
9	Conning tower superstructure		14.1

Type XXIII section description

Section	description	weight (tons)	length (meters)
1	Stern, steering installation, silent speed motor, gearing	11.5	9.2
2	Main engines and motors	14	6
3	Control room, forward living quarters (part)	18	7.5
4	Bows with torpedo tubes, forward living quarters (part)	16.25	10

On 30 September 1943 the building of some already obsolete boats was stopped (selected boats were already stopped on the 10th July). Subsequently, these boats were cancelled on the 6th November 1943 (the majority) or later (some particular boats). This applied to all Type VII C/42 boats and selected Type VII C/41, IX C/40, IX D/42, XVII B and XVII G boats.
Also, on the 6th November 1943 a final order for the construction of Type XXI boats was submitted to the following 3 shipyards:

Blohm & Voss, Hamburg	130 U-boats (U-2501 onwards)
Deschimag AG Weser, Bremen	87 U-boats (U-3001 onwards)
Schichau, Danzig (Gdansk)	70 U-boats (U-3501 onwards)

An order for the construction of Type XXIII boats was submitted slightly earlier, on 20th September 1943 to Deutsche Werft AG, Hamburg (U-2321 onwards) and later on 7th July 1944 to Germaniawerft, Kiel (U-2332-3, U-4701 onwards).
It is interesting to note that there had been some preliminary orders for Type submitted earlier, to other shipyards (e.g. order dated 6th July 1943 to Deutsche Werft AG for 24 Type XXI boats, cancelled on 30th September 1943).
From February 1944 onwards separate sections became systematically available. The first Electroboat to be laid down was a Type XXIII boat U-2321 on 10th March 1944. She was launched on the 17th April (after 38 days in the yard) and commissioned on 12th June 1944. The first Type XXI boat to be laid down was U-2501on 3rd April 1944. She was launched on 12th May 1944 (well ahead of the schedule) and commissioned on 27th June 1944.
The commission progress of Type XXI and XXIII boats is presented below:

Electroboat commission progress

Time	Type XXI	Type XXIII
June 1944	1	1
July 1944	3	3
August 1944	7	4
September 1944	8	6
October 1944	12	4
November 1944	13	7
December 1944	20	6
January 1945	22	12
February 1945	11	7
March 1945	18	6
April 1945	4	4
May 1945	-	1
Total	119	61

Type XXI commission progress

Time	Blohm&Voss	AG Weser	Schichau	Total
June 1944	1		-	1
July 1944	1	1	1	3
August 1944	3	3	1	7
September 1944	5	1	2	8
October 1944	6	3	3	12
November 1944	6	3	4	13
December 1944	6	6	8	20
January 1945	5	11	6	22
February 1945	5	6	-	11
March 1945	6	7	5	18
April 1945	4			4
May 1945				-
Total	48	41	30	119

Type XXIII commission progress

Time	Deutsche Werft AG	Germaniawerft	Total
June 1944	1	-	1
July 1944	3	-	3
August 1944	4	-	4
September 1944	6	-	6
October 1944	4	-	4
November 1944	6	1	7
December 1944	5	1	6
January 1945	9	3	12
February 1945	4	3	7
March 1945	3	3	6
April 1945	3	1	4
May 1945	-	1	1
Total	48	13	61

It is interesting to compare the technical data of both types of Electroboat and The Type XVIIB Walter U-boat:

	Type XXI	Type XXIII	Type XVIIB
Displacement surfaced (tons)	1621	232	312
Displacement submerged	1819	256	345
Dimensions (meters) - length	76.7	34.1	40.9
beam	6.6	3.0	3.4
draught	6.3	3.7	4.7
Machinery	2-shaft 6-cylinder MAN diesel/electric motors 4500/5000 bhp/shp silent speed electric motors 226 shp	1-shaft 6-cylinder MWM diesel 576 bhp AEG main electric motor 580 shp BBC silent speed electric motor 35 shp	Walter single-shaft turbines 2500 shp 8-cylinder Deutz diesel motor 210 bhp electric motor 77 shp
Fuel Capacity (tons)	250	18	75 (Perhydrol)
Batteries		62 double-cell 2x21MAL 740 E/23 5400Ah	4560 Ah
Maximum speed (knots) - surfaced	15.5	10.0	8.5
submerged	17.0	12.5	21.5 Walter 4.5 electric
max schnorkel speed		10.75
max silent speed		4.5
Endurance (miles) - max surfaced	15,500 @ 10 knots	4,450 @ 6 knots
surfaced	11,500 @ 12 knots	2,600 @ 8 knots	3,000 @ 8 knots
max sustained surfaced	5,100 @ 15.5 knots	1,350 @ 10 knots
max schnorkel endurance		3100 @ 6 knots
Endurance (miles) - max submerged	365 @ 5 knots	194 @ 4 knots
submerged	110 @ 10 knots	43 @ 10 knots	150 @ 20 knots
max sustained submerged		21 @ 12 knots	40 @ 4.5 knots electric
Diving depth - safe
Diving depth - max
Armament	6 bow tubes 23 torpedoes 2 twin 20 cm AA (3cm on later models)	2 bow tubes 2 torpedoes no guns	2 bow tubes 4 torpedoes no guns
Crew	57	14	19

It is important to remember that although the Walter U-boat possessed greater maximum speed and range, it was only of single use. Once the Perhydrol fuel was burn out, the boat could only bank on the conventional diesel-electric propulsion. The Electroboats could always recharge the batteries and therefore could benefit from the high underwater speed many times. On the other hand, the maximum speed was needed only for an attack - and with just 2 torpedoes the Walter U-boat indeed could practically attack only once. But having an ability to sprint away in the event of danger is always an advantage in the submarine warfare and therefore the Electroboats offered steady safety in comparison to the Walter ones.

3. Getting ready

The initial trials with the first available Type XXIs showed that the theoretical performance was almost met. The full submerged speed was slightly lower (17 instead of 18 knots) and could be maintained for a shorter time (60-80 minutes instead of 100). Overall, the performance was outstanding and offered much better prospects for attacking convoys and evading escorts than conventional U-boats.
At the silent submerged cruising speed the Type XXI had to schnorkel for only 3 hours a day to keep the batteries charged. This speed of 5 knots with a range of 365 miles meant that a U-boat would pass the dangerous waters between Norway and Iceland in 5 days schnorkeling shortly only 5 times. The radar-search receiver Tunis fitted to schnorkel and anti-radar rubber coating offered additional safety. Even when located, an alteration of speed and course would help to evade escorts or aircraft-dropped sonar buoys. When escaping at high speed, the Type XXI was almost as fast as most of the Allied escorts and bubbling of water rushing along the hull would make ASDIC location difficult. The potential area where a hunted Type XXI, escaping at the silent speed of 5 knots, would be forced to raise the schnorkel again was some 10-13 times greater than an area for conventional U-boat (escaping at 2 knots with a range of 100 miles). With the existing anti-submarine forces search abilities a chance for a kill was therefore greatly reduced.
The attack tactics was based on the following principles:

• location of a convoy by the listening device
• high-speed approach to the convoy
• penetration of the escort screen at silent speed and maximum depth
• getting underneath the convoy
• collecting firing data for the LUT looping torpedoes by echo-ranging
• firing spreads of torpedoes in order to cover the whole convoy

Special equipment was provided to facilitate the tactics, in particular a special echo-ranging plotting-table and an echo-ranging data converter which automatically calculated and set torpedo firing parameters. Due to the quick reload mechanism the Type XXI would need only one convoy encounter to fire all the torpedoes.
The preparation of the battle instructions for Electroboats was an interactive process with constant feedback and verification coming from the training units. The final battle instructions were written by experienced commanders: Erich Topp (for the Type XXI) and Carl Emmermann (for the Type XXIII). Others contributed though, among them Emil Klusmeier who later volunteered for a command in order to verify his ideas in practice and with U-2336 scored hits.
Although the first Type XXI was launched almost on time, the Electroboat building programme was eventually delayed by various means and the planned production figures had not been met. The following is the summary and status at the end of the war:

	Type XXI	Type XXIII
Planned for delivery by 1/05/45	381	95
Not produced because of the internal organization defects	202	13
Not produced because of Allied bombing on shipyards	60	19
Commissioned	119	61
Destroyed after commission  (trials, training, transit)	20	2
Training, fitting-out or on trials	86	38
Almost ready for combat	12	15
Fully ready for combat	1	6

The failure to achieve the objectives was mainly caused by organization troubles, faulty design and bad workmanship. It was particularly annoying, when sections did not fit to each other because the specified tolerances were exceeded. All these took place mainly in the first half of 1944 and was fixed in the second half of the year. At that time, however, the Allies realized the danger and started regular bombing raids, particularly on shipyards and water transport installations (needed for transportation of massive Type XXI sections).

Training for the new boats

Further delay in the project was caused by the extended training required for crews. The complexity of the design and new tactics meant that 6-7 months of training was required instead of usual 3-3.5 needed for conventional U-boats. Moreover, the training facilities were affected by the Allies actions, particularly the mining of the Bay of Danzig, the primary trial and training waters. The first mines were laid on 26/7 August 1944 by Bomber Command and continued regularly that eventually lead to the total abandoning of the area. The trials and tests were moved to the Bay of Luebeck which was much inferior, particularly because the area was within the range of Coastal Command.
The disruption of training caused that the Type XXI boats with practically one exception could not became fully operational in early 1945. Also, a number of boats that almost finished their training and awaited transfer to the Norwegian bases were lost in the dangerous Bay of Luebeck.

Operational Type XXI boats

The following Type XXI U-boats were almost ready for operations (on passage or in the operational bases, undergoing final preparations):

Place	Flotilla	Boat	Commander
in transit	11th Flotilla Bergen	U-2503 *	Oblt Raimund Tiesler
Bergen	11th Flotilla Bergen	U-2506	Kptlt Horst von Schroeter
Bergen	5th Flotilla Kiel	U-3514	Oblt Guenther Fritze
Stavanger	4th Flotilla Sttetin	U-3035	Oblt Ernst-August Gerke
Kristiansand	31st Flotilla Hamburg	U-2529	Kptlt Fritz Kalipke
Horten	11th Flotilla Bergen	U-2502	Kptlt Heinz Franke
Horten	11th Flotilla Bergen	U-2513	Korvkpt Erich Topp
Horten	11th Flotilla Bergen	U-2518	Kptlt Friedrich Weidner
Horten	4th Flotilla Sttetin	U-3017	Oblt Rudolf Lindschau
Horten	4th Flotilla Sttetin	U-3041	Kptlt Hans Hornkohl
Horten	5th Flotilla Kiel	U-3515	Oblt Fedor Kuscher
Wilhelmshaven	11th Flotilla Bergen	U-3008	Kptlt. Helmut Manseck

* U-2503 was badly damaged by aircraft on 3rd May 1945 and later scuttled.
The following was the only one Type XXI U-boat fully ready for operations at the end of the war:

Bergen

11th Flotilla Bergen

U-2511

Korvkpt Adalbert Schnee

It is sometimes reported that U-3008 also was ready for operations. She indeed sailed from Wilhelmshaven on 3rd May 1945, when the artillery bombardment was already heard. The U-boat may probably been supposed to call in one of the Norwegian ports for final provisioning before the patrol. In the North Sea, shortly after the order to surrender which was issued on 4th May 1945, she encountered a convoy, made a pass under it and sailed away undetected.

First war patrol by type XXI boat, the U-2511

U-2511, with a crack crew, sailed from Kiel on 16 March 1945 for the Norwegian base Horten in Norway. The war patrol was supposed to start on 26 March, but during deep dive test she sustained a periscope damage and was delayed. She sailed from Horten on the 18 April she was forced to put to Bergen on 21 April, due to diesel troubles. At last she sailed on 30 April 1945 with the orders to go to the Caribbean.
The first contact with the enemy was made on 1 May. On the following day U-2511 was detected by an escort group north of Scotland but easily got away with the increased underwater speed. She evaded other ships, too, as her objective was to get to the operation area first. Depth-charges were dropped but were helplessly wide. Soon after receiving the surrender message on 4 May 1945, U-2511 detected a Suffolk class cruiser, HMS Norfolk, with destroyer escort at a long range. She made a text-book approach, closing at high-speed first, then diving deep and passing the destroyer screen at silent-speed. Finally, Schnee had the cruiser in sights 500 meters away with a perfect attacking position inside the destroyer screen and undetected - impossible  to miss. U-2511 did not fire but dived deep again, and still undetected returned to base, arriving at Bergen on 5 May 1945.

4. Aftermath

What may be a sort of surprise is that the technology used in the design was by no means new. To characterize the concept, the following 3 features should be listed:

1. streamlined hull
2. snorchel
3. huge battery capacity

The benefits of the streamlined hull had been known long before the era of Electroboats. In fact, the very first submarines including original Holland's vessel were more streamlined than their WW1 and WW2 successors. Schnorchel was developed in the 30's by the Dutch, but the concept was known to the others. Adding more battery capacity is just a matter of space, not technology.
Therefore, it should be noted that the technology used for Electroboats was actually available already in the 30's. Why it was not exploited? There was no need to do so as long as the U-boat was safer and performed better on the surface at night than under the surface. This was clearly demonstrated in the first few years of the U-boat War. Only when the relative safety of staying on the surface was taken away by radar and aircraft, the German Naval High Command started looking for an alternative solution.
The reason for the late introduction of Electroboats should be primarily related to the underestimation of radar technology. In this particular field the Germans were significantly behind England. Had the German radar technology been more advanced, it would have probably been realized that it was just a matter of time before the small silhouette of the surfaced U-boat was indeed big enough for the radar to be located. And then the Electroboats could have come earlier.
Also, outstanding was the production process of the Electroboats, particularly the larger one. It was one of the few examples of the implementation of mass-production principle by the German industry during the Second World War. Of course, this too was affected by the Allied bombing, but the final number of commissioned Electroboats should be regarded as high. It is again a kind of surprise that the mass-production concept was not adopted earlier, particularly for the conventional U-boat production. A high number of conventional U-boats in the second half 1941, when the British counter-measures were not fully developed yet, instead of 1942, certainly would have made a difference.
The experience of U-2511 clearly demonstrates the outstanding performance of the Type XXI and  it is certain, that the Allied navies had no ready answer to the new threat. The operations of the Type XXIII constitute yet another proof of the fighting qualities of the Electroboats. Had the Allied progress on land been slower, the Type XXI U-boats might have appeared in numbers great enough to paralyze the Atlantic communication routes, even in spite of the increased bombing of production and training facilities.

Electro boat diary:

November 1942	The birth of the Electroboat idea
January 1943	Theoretical calculations finished
June 1943	Design completed
July 1943	Project approved
September 1943	Conventional U-boat building programme limited
November 1943	Orders placed
December 1943	Production design completed
30 April 1944	First Type XXIII launched (U-2321)
12 May 1944	First Type XXI launched (U-2501)
12 June 1944	First Type XXIII commissioned (U-2321)
27 June 1944	First Type XXI commissioned (U-2501)
August 1944	First aerial mines in the Bay of Danzig
29 January 1945	First Type XXIII sailed on war patrol (U-2324)
February 1945	Testing and training transferred to the Bay of Luebeck
14 February 1945	First success by an Electroboat (U-2322)
30 April 1945	First Type XXI sailed on war patrol (U-2511)
7 May 1945	Last success of an Electroboat and in the war (U-2336)

 Source : www.uboat.net ,with necessary change.