From the tower aft the Type XXIII was all machinery. The forward quarter was all torpedo room and, except for a minuscule control room, the crew was squeezed above the banks of high-capacity battery cells. Note the single screw and unusual control surf aces.
Rather than search the Atlantic for convoys it may, in retrospect, have been more rewarding for the German submarine arm to develop tactics to tackle them at their known points of arrival and departure, despite the likely concentrations of escorts. A suitable vehicle would have been the Type XXIII, small and agile for shallow water operations and, like its larger cousin the Type XXI, packed with high-capacity battery cells for maximum underwater speed. Its hull had the ‘double-bubble’ cross section over the forward half but was internally framed and prefabricated in four sections. The partial length lower hull contained both batteries and some ballast and fuel capacity. A departure was the near abandonment of outer casing except in the transitional zones and this, together with a very low reserve buoyancy (the difference between surfaced and submerged displacements was only 24 tons) allowed for rapid crash-dive, times of less than 10 seconds being recorded, Even smaller than the Type XVII Walter boats, the Type XXIIIs also had a single shaft but a propeller proportionately larger in diameter for greater propulsive efficiency.
Though the boat was designed to operate submerged, its silhouette on the surface was very small, being little more than the slim tower with the attached low casing that enclosed the snort induction and engine exhaust arrangements. No guns were carried and, oddly, only two torpedo tubes. With no space inboard for orthodox loading, the boat needed to be trimmed by the stern to expose the bow caps. As no spares could be carried an extra two or four tubes forward would have been a bonus. As it was, attacks had to be carried out positively, from close range and with very fast or very stealthy disengagements, That this was possible was shown by the last U-boat attack in European waters, which occurred on 7 May 1945 well inside the Firth of Forth, when the U- 2336 sank two British merchantmen of an escorted convoy. One torpedo was used on each, fired on the strength of passive sonar bearings from ranges of less than 500 m (545 yards), By this time 62 type XXIIIs had entered service and their only losses had been to aircraft; it was fortunate for the Allies that the enemy’s training and dedication no longer matched his technology.
The first Type XXIII, U-2321, was launched from Deutsche Werft in Hamburg on April 17, 1944. It was one of six XXIIIs that went on operational patrol around the British Isles in early 1945. Forty-eight others followed from Deutsche Werft and 13 from Germaniawerft of Kiel. U-4712 was the last one launched, on April 19, 1945.
The first patrol of a Type XXIII began late in the war when U-2324 put to sea on January 29, 1945. U-2336 under the command of Kapitänleutnant Klusmeier sank the last ships lost in the war, on May 7, when he torpedoed a British and a Norwegian freighter inside the Firth of Forth.
None of the six operational Type XXIIIs — U-2321, U-2322, U-2324, U-2326, U-2329 and U-2336 — were sunk by the Allies but they sank or damaged five ships for a total of 14,601 tons.
Seven Type XXIIIs were lost to various causes.
* U-2323 was sunk by a naval mine on July 26, 1944.
* U-2331 was lost in a training accident on October 10, 1944.
* U-2338 was the only XXIII to be sunk by the enemy. British Beaufighter aircraft killed 12 crewmen and sank the boat east-northeast of Fredericia on May 4, 1945, before she ever went on combat patrol.
* U-2342 was sunk by a naval mine on December 26, 1944.
* U-2344 was rammed and sunk by U-2336 on February 18, 1945.
* U-2351 was paid off in April 1945 after bomb damage.
* U-2367 was rammed and sunk by an unidentified U-boat on May 5, 1945.
In early May 1945, 31 XXIIIs were scuttled by their crews. Twenty surrendered to the Allies and were sunk in Operation Deadlight. Only three — U-2326 (later British submarine N-35), U-2353 (later British submarine N-37), and U-4706 (later Norwegian submarine Knerten) — survived the war.
Specification
Type XXIII
Type: coastal submarine
Displacement: 232 tons surfaced and 256 tons submerged
Dimensions: length 34.10 m (112 ft 0 in); beam 3.00 m (9 ft 10 in); draught 3.75 m (12 ft 3 in)
Propulsion: surfaced diesel delivering 580 bhp (433 kW) and submerged electric motor delivering 600 hp (447 kW) or electric motor delivering 35 hp (26 kW) to one shaft
Speed: surfaced 10 kts and submerged 12.5 kts on main electric motor or 2 kts on creeping electric motor
Range: surfaced 2500 km ( 1,555 miles) and submerged 325 km (202 miles) at 4 kts
Armament: two 533-mm (21 -in) torpedo tubes (both forward) with two torpedoes
Complement: 14
