Not that grim. An RCAF Sunderland sunk a U-boat. Prohibited from landing to pick up survivors (too many to be able to fly, likelihood of being outnumbered and taken over), the Sunderland took a photo of the crew in their lifeboats. The U-boat crew later died to a man of exposure before they could be picked up. So the same scenario the U-boat crew likely participated in when sinking merchantmen. War is cruel.