The Electroboats

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: 

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: 

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: 

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

acquisition of raw materials and transport to steel works16 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,
130 U-boats
(U-2501 onwards)
Deschimag AG Weser,
87 U-boats
(U-3001 onwards)
Schichau, Danzig
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:

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
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.

... the Elektro boats are getting ready

The Electro boats