German ocean supply ships and stern refuelling

How did the German Navy refuel at sea, including Bismarck's possible refuelling options?

Germany used pre-positioned supply ships, but Bismarck's practical access to them is uncertain; the panel describes stern hose transfer as the likely technique.

Germany positioned merchant-type support ships in ocean areas where raiders could rendezvous with them; specialized submarine supply boats appeared later. The ability to refuel at sea did not guarantee that a suitable tanker was close enough for Bismarck to use. The panel is uncertain about the ships available and recalls some Atlantic support vessels being much farther west, beyond Greenland. Stern refuelling is offered as the probable method rather than established for a particular rendezvous. A buoy carries a light rope to the receiving ship, which uses it to bring across a heavier cable and then the fuel hose. The sequence resembles establishing a tow.