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.
Many additional ships that are not included in those totals were damaged, but were able to return to service after repairs. This list contains the approximately 100 ships over 10,000 tons that were either damaged or sunk by U-boats by torpedoes, submarine-laid mines, gunfire, or other means.