 Dönitz calculated 300 of the latest "Atlantic Boats" (the Type VII), would create enough havoc among Allied shipping that Britain would be knocked out of the war.This was in stark contrast to the traditional view of submarine deployment up until then, in which the submarine was seen as a lone ambusher, waiting outside an enemy port to attack ships entering and leaving.This had been a very successful tactic used by British submarines in the Baltic and Bosporus during World War I, but it could not be successful if port approaches were well patrolled.