The Type X was originally designed specifically to accommodate the newly developed Schachtmine A (SMA) moored mine.

[3] The initial design provided dry storage for the mines, which needed their detonators to be individually adjusted before launch; this submarine was projected to have displaced up to 2,500 tonnes.

[5] A total of eight Type XB boats were produced, which replaced the mine chamber of the projected Type XA with six vertical wet storage shafts in the forward section of the hull.

[1] At 2,710 tonnes submerged and fully loaded, they were the largest German U-boats ever built, and they had to sacrifice diving speed and agility.

The other type XB to survive was U-219 which reached Batavia (present-day Jakarta) in December 1944 with a cargo including dismantled V-2 rockets for Japan.