When transportation to America stopped in 1776, serious overcrowding of the prisons led to the introduction of decommissioned navel vessels, or Hulks, to be used as floating gaols. The first of these floating prisons was placed on the River Thames at Woolwich and also in Plymouth Harbour. The conditions on the hulks were even worse than in the gaols with mortality rates at around 30%. The first of the vessels to be commissioned were Justitia, Censor, Ceres, Fortunee and Dunkirk. After the commencement of transportation to New South Wales in 1788, two more vessels, Stanislaus and Leon, were added to the fleet. In 1791 the number of hulks fell, with the discharge of Justitia, Ceres and Dunkirk in the March of that year, after the departure of the Third Fleet for New South Wales.