Page:The Development of Navies During the Last Half-Century.djvu/157

 improved machinery increased the speed to 15 knots. The defect of such vessels is the absence of stern fire, and with 6000 tons a second turret aft seems desirable.

But strong pressure was all the time being put on the Admiralty to build a vessel in which guns should have no place, and the most persistent advocate was Admiral Sir George Sartorius, who appears to have formed an exaggerated view of the ram as a weapon. The result was the construction of the 'Polyphemus.' The leading features of her design were a low hull, exposing but a small mark to an enemy's fire, the portion above water being shaped like a turtle's back, and covered with thin armour to deflect any projectile that might strike it; great speed, by the adoption of special machinery, a powerful ram, and a torpedo equipment. The only ordnance was to consist of a few light guns for repelling boat or torpedo attack. These are mounted on a superstructure necessary for carrying the boats and working the ship at sea. A special point in her design was the formation of the keel as a rectangular groove, in which are placed lengths of cast-iron ballast. This extra weight, amounting to about 300 tons, is not permanently fixed, but can be dropped when required, so as to lighten the vessel if any injury is received reducing the buoyancy. All or portions of it can be released from the conning station. While the vessel is intact the ballast assists in keeping the greater portion of the hull immersed, making a difference of about 12 in. in the draught. Though the 'Polyphemus' was commenced in 1878, difficulties with the