November 1842, aboard the Somers in the African Squadron, commander Alexander Slidell Mackenzie ordered the arrest of three crewmen who were plotting to take control of the ship. The three crewmen were convicted; they were hanged on 1 December. This is the only occurrence of Maritime Mutiny at Law in the history of the United States Navy. Commodore Perry was placed in command of the African Squadron in 1843. Ships which captured slavers while deployed with the African Squadron include Yorktown, Constellation, and the second Constellation, which captured Cora on 26 September 1860, with 705 Africans on board. The first San Jacinto captured the brig Storm King on 8 August 1860, off the mouth of the Congo River, with 616 Africans on board. In her final act, Constitution captured H.N. Gambrill in 1853. The Navy attempted to intercept slave ships from 1808 (or 1809) to 1866. A small number of ships were intercepted; some of those ships were carrying Africans destined to be sold into slavery, while other suspected ships which had none on board were captured and escorted away from the coast of Africa. Black Ivory The Louisiana Purchase in 1803 created a great demand for more slaves to work in the vast new area. Jean Lafitte was a pirate who brought many slaves to the United States and sold them through an organised system established at New Orleans that included many merchants from the vicinity. After he helped Andrew Jackson during the War of 1812, President James Madison issued a proclamation early in 1815 granting him and his men pardons for their misdeeds. The United States Navy's Africa Squadron, Brazil Squadron, and Home Squadron were assigned the task of intercepting the ships which were bringing Africans across the Atlantic Ocean to the slave markets where black ivory found numerous customers. Since the War for Independence had been costly, no American warships were constructed between 1783 and 1795. The Navy Department was created on 30 April 1798, four years after President George Washington had communicated with Congress and expressed his alarm at the outrageous behaviour of Algeria. On 27 March 1794, following communication with President Washington, Congress authorised the purchase or construction of six frigates. These ships included the first Constellation, launched 7 September 1797 and Constitution, a ship that would be briefly employed in the African Squadron. Few new ships were built in the United States after 1801