 The centre @-@ battery was the simpler and , during the 1860s and 1870s , the more popular method . Concentrating guns amidships meant the ship could be shorter and <unk> than a broadside type . The first full @-@ scale centre @-@ battery ship was HMS Bellerophon of 1865 ; the French laid down centre @-@ battery ironclads in 1865 which were not completed until 1870 . Centre @-@ battery ships often , but not always , had a recessed freeboard enabling some of their guns to fire directly ahead . 
