During the First World War, both Britain and Germany relied on imports for food and vital raw materials, much of which came from the Americas via the Atlantic Ocean.
Britain and Germany both tried to blockade each other, using their war ships to block the merchant ships from reaching their home ports. The British Royal Navy was superior in numbers to the German navy, and had ships around the world operating from bases across the British Empire. Germany, however, operated a policy of unrestricted submarine warfare, attacking merchant ships.
The submarines were known as U-boats, and the U-boat campaign was waged both officially and unofficially by Germany between 1915 and 1918 against Britain and her allies. One of the most infamous attacks was the sinking of the passenger liner RMS Lusitania in May 1915. Torpedoed without warning, the attack resulted in the loss of 1,198 mainly civilian lives.
The number of British merchant ships lost during the war increased in frequency as time went on.
In 1914 65 ships were lost, in 1915 278 ships were lost, in 1916 it was 896 ships. In 1917, 155 ships had already been sunk by the start of March. The sinking of the Otaki, in which six lives were lost, was the 33rd of a total 127 vessels sunk in March alone.