the squadron also used Ascension Island as a supply depot, before this moved to Cape Town in 1832. As the Royal Navy began interdicting slave ships, the slavers responded by adopting faster ships, particularly Baltimore clippers. At first, the Royal Navy was often unable to catch these ships. However, when the Royal Navy started to use captured slaver clippers and new faster ships from Britain, the Royal Navy regained the upper hand. One of the most successful ships of the West Africa Squadron was such a captured ship, renamed . She successfully caught 11 slavers in one year. By the 1840s, the West Africa Squadron had begun receiving paddle steamers such as , which proved superior in many ways to the sailing ships they replaced. The steamers were independent of the wind, and their shallow draught allowed them to patrol the shallow shores and rivers. In the middle of the 19th century, there were around 25 vessels and 2,000 personnel with a further 1,000 local sailors involved in the effort. Britain pressed other nations into treaties that gave the Royal Navy the right to search their ships for slaves. As the 19th century wore on, the Royal Navy also began interdicting slave trading in North Africa, the Middle East, and the Indian Ocean. The United States Navy assisted the West Africa Squadron, starting in 1820 with USS Cyane, which the US had captured from the Royal Navy in 1815. Initially the US contribution consisted of a few ships, which comprised the Africa Squadron after the Webster-Ashburton Treaty of 1842. In 1867, the Cape of Good Hope Station absorbed the West Coast of Africa Station. In 1942 during World War II the West Africa Station was revived as an independent command until 1945. Impact The West Africa Squadron seized approximately 1,600 ships involved in the slave trade and freed 150,000 slaves who were aboard these vessels between 1807 and 1860. Robert Pape and Chaim Kaufmann have declared the Squadron the most expensive international moral action in modern history. Liberated slaves While liberated slaves were returned to Africa, those who came from inland regions could not be returned to their place of origin. They often suffered in appalling conditions on the return voyage, or while waiting for courts to adjudicate their case. It is estimated as many as 25 percent of those who could not be returned to their place of origin