The Type 404 Elbe class replenishment ships of the German  Navy were built to support its squadrons of Fast Attack Craft, submarines  and minesweeper/hunters, as such they are  usually referred to as tenders.
The ships carry fuel, fresh water, food, ammunition  and other matériel. They also have a medical  station aboard but doctors are not part of their standard complement  and will have to be flown in. The tender also manage waste disposal for the ships they support at sea and can  carry out minor repairs of assigned ships. For this purpose Elbe class  tenders assigned to FAC squadrons, for example, carry the SUG repair and support  shop specialized for these boats on their deck in a set of 13 standard  containers.
Extensive communication gear and accommodations enable them to serve  as squadron flagship.  While in general all Elbe class tenders are quickly configurable to  be reassigned to support other squadrons, one of the six ships is  usually modified to support German submarines - carrying batteries for  reloading for example. This ship - currently A515 Main - while  still being of the same class, and easily reconfigurable - is often  named as a separate "sub-class" due to this larger modification.  The ships are all named after German rivers
Ships of the class
 A 511 Elbe
A 512 Mosel
A 513 Rhein
A 514 Werra
A 515 Main
A 516 Donau
Fgs Elbe is seen here departing Faslane with her chicks in the background
A few days later she is alongside in Leith