Navicert
The navicert, short for navigation certificate, also known as a "Letter of Assurance", was a form of commercial passport issued to allow ships to pass through blockades without inspection. This was of particular relevance during the British naval blockades of Germany in World War I and World War II. == Background == Navicerts were introduced at the suggestion of US Consul General in London Robert Peet Skinner and first issued in March 1916, as a method of reducing the inconvenience of the blockade to neutral trade.