During the Second World War, Tristan was commissioned by the Royal Navy as a top-secret naval station code-named Job 9 and later renamed HMS Atlantic Isle. Its role was to monitor U Boats (which were required to maintain radio contact) and shipping in the South Atlantic Ocean.
In early May 1943, the island was assaulted by an easterly gale lasting four days. A week later four American liberty ships, all eastward bound, put to the island one after the other. They had suffered damage to their cargos and radio equipment.
Liberty ships were a class of cargo ship built in the United States during WWII. They have been described as the ships that won the war.
In 1939 the German Navy launched submarine warfare in the North Atlantic Ocean to enforce a naval blockade against Great Britain. The submarines sank great numbers of merchant ships approaching the British Isles.
If the United States entered the war cargo ships would be needed to ferry supplies to allies and the United States decided to modify the English design being used for the Lend-Lease ships as they could be mass produced and relatively cheaply meet the United States WWII maritime transport needs.
The new emergency cargo ships came to be known as the Liberty ships. Between 1939 and 1940 only 82 vessels were constructed but the Ship Warrants Act in 1941 gave the Maritime Commission power to allot ship construction priorities. The Maritime Commission established 18 new shipyards to work on these identical merchant ships and between 1941 - 1945 2710 Liberty ships were built (an average of three ships every two days). By 1944, the average time to build a Liberty ship was less than forty-two days. During the course of the war Liberty ships carried around two-thirds of all United States cargo.