‘Scuse me. In at least one instance, a U-boat that sunk a liner/freighter, with lots of civilians on it, took the wounded aboard, tied lines to all the lifeboats, rendered aid, including water and food; began towing them, and called [in clear] his position to the Brits in [I believe] South Africa, explaining the situation. For his trouble, the British attempted to bomb him. He released the tow ropes and submerged.
As a result, Doenitz issued orders that the U-boats were not to engage in similar acts again.
Skippers had a moral obligation to take their subs out and sink them thereby avoiding all these accusations that they snuck up on civilians and murdered them on the highseas.
Actually, Doenitz issued orders not to render assistance to sinking victims because captains doing so endangered their ships and interfered with fulfilling their mission, which was sinking more ships. On at least one instance a U-Boot was sunk after rendering assistance, although cause and effect are not clear. Most of the time U-Boots approached on the surface (for purely tactical reasons) and victims had lots of time to radio their positions and plight, bringing in whatever destroyers or aircraft were in the area.
Stopping to render assistance may have been the exception, rather than the rule, but it was common enough that Donitz felt compelled to issue the order to refrain. American commanders in the Pacific felt no need to issue similar orders to U.S. submarines.