Using the plans for the planned but never produced TYPE X-A, the TYPE X-B was a much improved design. This boat boasted more mine-laying tubes than planned in the TYPE X-A, and added two stern tubes. In the X-B, mines were stored in six internal shafts forward (three mines per shaft) which projected above & below the pressure hull; and there were 24 external mine shafts (two mines per shaft), 12 per side. There were torpedo reloads stowed inside the pressure hull as well as externally, below the decking.

While the TYPE X-B was designed initially as a mine laying submarine, the Allies excellent ability to detect and neutralize enemy mines made this application futile, so most of the missions of the TYPE X-B boats were to supply FrontBoots instead. Some were used for clandestine missions; the most notable was U-234, which departed Kiel bound directly for Tokyo with a cargo of the newest electric torpedoes, two Me 262 jet fighters in crates with the technical data for the Japanese to build these fighters, the Commanding General of the Luftwaffe, a Naval Fleet Judge, top-level scientists - and 560 kilos of Uranium Oxide for the Imperial Japanese Army for their atomic bomb!

Displacement 1,763/2,177 tons
Dimensions 294.75 x 30.25 x 13.5 feet
Power twin-shaft diesel/electric
(diesel) 4,200hp
(electric) 1,100hp
Speed
(diesel) 16.5 knots
(electric) 7 knots
Bunkers 368 tons
Radius
(diesel) 14,550 miles @ 12 knots
(electric) 93 miles @ 4 knots
Tubes
(foreward) none
(aft) two (21 inch) (carried fifteen torpedoes total)
Guns single 4.1 inch deck gun on foredeck
AA Guns single 3.7cm and single 2.0cm
Mines 66
Crew 52

NOTE - Eventually schnorkel was added to most TYPE X-B boats; the deck gun was removed; twin 2.0cm guns replaced the single mount.