Instinctive behavior occurs when an animal has a particular internal state while it is in the presence of a specific external stimulation called a releaser or a sign stimulus.
How many ships did the U-boats sink? During the war the U-boats sank about 2,779 ships for a total of 14.1 million tons GRT. This figure is roughly 70% of all allied shipping losses in all theatres of the war and to all hostile action. The most successful year was 1942 when over 6 million tons of shipping were sunk in the Atlantic.
If under attack by surface ships, there was some chance for some of the crew to escape and be rescued by the attackers: three of four u-boats sunk off the US coast with survivors were sunk by surface ships, compared to only one u-boat sunk by aircraft attack with survivors. U-166 - sunk 30 July 1942 in the Gulf of Mexico. No survivors, 52 dead.