While working on the Type XXI design a naval construction director called Oelfken came across the type XXII design by Hellmuth Walter, which was a small coastal U-boat with closed-cycle drive, and considered the possibilities for an electro-boat of about the same size. The idea for a coastal electro-boat was accepted by Doenitz with two provisos, firstly that the design be split up into sections which could be transported by rail and secondly that 7 metre torpedoes be used rather than the 5 metre type favoured by Walter. The coastal electro-boat or Type XXIII had a submerged displacement of 275 tons compared to the 1819 tons of the Type XXI. Like the Type XXI the Type XXIII had a large battery capacity utilising a figure of 8 double-bubble cross section for part of its length. The Type XXIII was a single propeller design with electric and diesel engines of around 600 hp and a creeping electric motor for speeds up to 4.8 knots. The single hull design with a minimal free-flooding volume achieved an underwater speed of 12.5 knots and a snorkeling speed of 10.75 knots. The maximum speed on the surface was less than expected due to a wave coming over the bows greatly increasing resistance and limiting the speed to about 9.7 knots. The design featured a knife-edge stern and a single rudder behind the propeller, and was very manoeuvrable with a small turning circle. Stern hydroplanes were fitted low down in front of the propeller and bow hydroplanes were fitted when it had been established that they were necessary for slow speed manoeuvring. With a small difference between surfaced and submerged displacement, about 41 tons, the Type XXIII could dive very rapidly in about 10 seconds. The normal deep diving depth was about 80 metres.
Originally the submarine was intended to be transported by rail to various ports in German occupied territories, where the sections would be assembled. However following German military reversals, by 1944, it became clear that all the boats would be assembled in Germany. There were 4 sections plus the conning tower. Late in the design stage the boat was found to be too heavy but this was solved by inserting an extra 2.2 metre long section between the control room and the bow section. The Type XXIII had fewer teething troubles than the Type XXI partly because more well-tried components were used. For instance the diesel engine had been used before in diesel generator sets and the electric motor was based on that used in the Type VIIC. The Type XXIII carried only two torpedoes with no reloads. The tubes were loaded externally through the bow caps after trimming the boat down by the stern. The above was a major limitation and a relatively small increase in length would have allowed 4 torpedoes to be carried.
When the war ended on May 8 1945 a total of 62 Type XXIIIs had entered service of which 18 were stationed in Norway and the rest in northern Germany. Ten boats are known to have carried out operational missions sinking five Allied merchant ships, GRT 14,345, for no loss to the attacking submarines.
Originally the submarine was intended to be transported by rail to various ports in German occupied territories, where the sections would be assembled. However following German military reversals, by 1944, it became clear that all the boats would be assembled in Germany. There were 4 sections plus the conning tower. Late in the design stage the boat was found to be too heavy but this was solved by inserting an extra 2.2 metre long section between the control room and the bow section. The Type XXIII had fewer teething troubles than the Type XXI partly because more well-tried components were used. For instance the diesel engine had been used before in diesel generator sets and the electric motor was based on that used in the Type VIIC. The Type XXIII carried only two torpedoes with no reloads. The tubes were loaded externally through the bow caps after trimming the boat down by the stern. The above was a major limitation and a relatively small increase in length would have allowed 4 torpedoes to be carried.
When the war ended on May 8 1945 a total of 62 Type XXIIIs had entered service of which 18 were stationed in Norway and the rest in northern Germany. Ten boats are known to have carried out operational missions sinking five Allied merchant ships, GRT 14,345, for no loss to the attacking submarines.
Specifications
Displacement
Surfaced: 234 tons
Submerged: 275 tons
Dimensions
Length: 34.7 metres
Beam: 3.0 metres
Draught: 3.7 metres
Propulsion
Diesel: One MWN 6-cylinder, 4-stroke RS-34-S unsupercharged diesel; 580 hp
Electric motor/generator: One AEG GU 4463-8 double-armature; 580 hp
Electric creep motor: One BBC GCR-188 single-commutator electric motor; 35 hp
Battery: One 62-cell AFA 2x21 MAL-740E battery; 5400 amp hour
Fuel capacity: 18 tons
Performance
Maximum speed
Surfaced: 9.7 knots
Snorkel: 10.75 knots
Submerged: 12.5 knots
Creep: 4.8 knots
Range
Surfaced: 2600nm at 8 knots
Submerged: 175nm at 4 knots
Crash dive: 9 seconds
Weapons
Bow tubes: Two 21 in (533mm)
Stern tubes: None
Torpedoes carried: Two
Guns: None
Officers and Crew
2 officers, 12 enlisted men
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