[bigboywooly]

http://uboat.net/types/viid.htm

http://www.uboataces.com/uboat-type-vii.shtml

The Type VIID was a specialized minelayer designed to lay SMA type mines in British coastal waters. These SMA mines had to be deployed vertically and differed from TMA and TMB mines which were torpedo launched.
Using the layout of the VIIC, a new section was inserted aft of the control room. Five vertical mine launchers, each comprising of three SMA mines were housed in this new section. Further space in this section was used to accommodate additional bunks and two refrigerators. The saddle tanks were also lengthened, allowing a higher capacity of diesel fuel.
The Type VIID was unique in its ability. Because the mine launchers were housed in a completely new section, this meant that the existing structure of the boat remained unchanged. Thus the torpedo and armament functions of the boat were fully operable, allowing the boat to serve a dual role – as minelayer or attack boat. However, due to its increased size and weight, it performed marginally poorer in maneuverability, speed, and diving time. Range was somewhat greater due to the lengthened saddle tanks.
A total of six Type VIIDs were commissioned between August 1941 and January 1942.

my bad - they were the SMA mines fired vertical