Type XB U-Boats

The Type XB U117 viewed from above. The mine shafts on either flank are plainly visible.

Dimensions: 89.8 metres x 9.2 metres x 4.7 metres (draught).

Displacement: 2177-tonnes dived            Complement: 5 officers, 47 crew.

Armament: 2 x 53.3cm (21”) torpedo tubes at stern below the designed waterline.
                   15 x torpedoes
                   Two groups of 12 mineshafts each side of the outer hull (48 SMA mines).
                   Six mineshafts in forward outer hull (18 SMA mines
                   1 x Utof 10.5cm/45 deck cannon (200 rounds) ¾ removed from 1943-44.
                   1 x 3.7cm AA cannon (2 500 rounds)
                   1 x 2cm AA cannon (4 000 rounds) ¾ increased to two cannons 1943-44.

Propulsion: 2 x Germaniawerft F46a 9pu 9-cylinder 4-stroke 2100 horsepower supercharged diesels, in diesel room housed within compartment three. 2 x AEG GU 720/8 double 287 horsepower electric motors in compartment two. 2 x 124-cell AFA 33 MAL 800 accumulator batteries in battery boxes below compartments four and six. (1960 amps/hour).

Speed: 16.4 knots surfaced/7 submerged.

Laid down as ocean-going minelaying submersibles, these U-boats were originally designed in 1938, developed from a combination of the Type I and Type XA designs (the XA never got as far as production - the boat modified into the XB model). They had a double hull divided into seven watertight compartments. Trim tanks were housed in compartments one and two, while diving tanks and fuel were contained in the outer hull, almost square when viewed sectionally. Pressure tight regulating tanks and further fuel oil bunkers were contained amidships, additional diving tanks located in the bow and stern.

During the course of the war modifications to the submarines' conning tower were the same as for Type VII and Type IX U-boats. A hinged schnorkel was fitted from mid-1944 on the starboard after edge of the conning tower casing.

These submarines were the first dedicated mine-laying U-boats built since the First World War and the largest built by Nazi Germany. Designed to carry 66 SMA mines (Schachtmine or Shaft Mine) and 15 torpedoes, the 2.15 metres long 1.33metres diameter mines stored in 12 vertical shafts on each side of the hull. However, the mines were discovered to be defective, design faults found to cause premature explosions, requiring several months of modification to correct, an embargo placed on their use until March 1943 (U117 was the first U-boat to deploy the redesigned SMA off the Moroccan coast after transfer to Bordeaux's 12^th U-Flotilla). Consequently the four Type XB U-boats constructed served as U-tankers in the Milchkuhs (Milk Cow) role, able to carry 240-tons of fuel for attack U-boats to use.