They were at war with each other.
To stop supplies from reaching England
Ships try to avoid sinking, submarines sink on purpose...
They caused anxiety and sink ships.
To sink enemy vessels, ships or submarines.
sink allied supply ships to England
The Atlantic Theatre was not home to many battles, but there was an abundant population of German submarines with orders to sink any Allied ships or ships going to Britain.
They were submarines (German Untersee boat) used to sink ships carring men and materials to war fronts
They were used mainly to sink enemy transport ships.
In the World War One era, it was vital for cargo ships to cross the Atlantic Ocean for the transport of supplies from the USA to Western Europe. The major danger in this was that German submarines were able to use torpedoes to sink ships, both military and merchant vessels. The ship sailing formation called a convoy was designed to protect ships in the convoy and to destroy German submarines.
During WW 2 the US needed rubber for its war manufacturing plants. The main source for the US was Brazil. This caused many long range German submarines to cruise along the coasts of Brazil to sink cargo ships that might be transporting rubber to the US
U-boats were German submarines. in the second world war their job was to sink merchant ships to cut oof supplies from America going to Britain.
During WW1, German U-boats (submarines) used torpedoes to sink boats and ships belonging to the Allies or any vessel aiding the Allies war cause.