HAM, a small town of northern France, in the department of Somme, 36 m. E.S.E. of Amiens on the Northern railway between that city and Laon. Pop. (1931) 2,787. It stands on the Somme, dominated by a castle which was built in the 1 oth century, now in ruins. The castle of Ham has frequently been used as a state prison both in ancient and modern times, and the list of prisoners include Joan of Arc, Louis of Bourbon, the ministers of Charles X., Louis Napoleon, and Generals Cavaignac and Lamoriciere. During 1870-1871 Ham was several times captured and recap tured by the belligerents. From the 9th century onwards it was the seat of a lordship which, after the extinction of its hereditary line, passed in succession to the houses of Coucy, Enghien, Luxem bourg, Rohan, Vendome 'and Navarre, and was finally united to the French crown on the accession of Henry IV. The church, damaged during the war 1914-1918, includes 12th century effigies of the Lords of Ham in its ancient crypt. Ham is at an im portant position on the Somme and suffered greatly during the campaign on the Western front in 1914-1918, especially during the retreat in the spring of 1917. It was in this vicinity that tanks were first used.