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.
When the First World War began the German armed forces had 29 U-Boats at their disposal. In the first 10 weeks of the conflict they sank five British cruisers. Between October 1916 and January 1917 a grand total of 1.4 million tons of allied shipping was lost to the U-Boats.