Vickipedia

SPI’THEAD FORTS. The troubled state of European politics which gave rise in 1859 to the Volunteer movement, led also to the recommendation of an extensive plan of defence for the arsenals and coast. A Board of Commissioners drew up a scheme for these defences, to cost about £5,000.000, of which a sum of £2,000,000 was for Portsmouth, Spithead, and the neighboring coast. At present, the entrance to the important arsenal and dockyard at Portsmouth is defended by Fort Moncktou on the Gosport side, Southsea Castle on the opposite side, Cumberland Fort at the entrance to Langston Harbor, Lumps and Eastney Forts between the two last named, and some defensive lines between the island of Portsea and the mainland. £580.000 was voted in 1860 as a beginning, to increase the number and strength of these forts, to build detached forts on shoals in the sea between the mainland and the Isle of Wight, and to raise fortified lines on Portsdown Hill (the principal work being Fort South-wick), wholly northward of Portsmouth Harbor. The works were commenced; but the often-conflicting lessons furnished by the American war led to much delay and endless variations of plan.

The National Defence Commissioners had proposed five advanced forts on the shoals known as Horse Sand, Noman or No Man’s Land Shoal, Sturbridge Shoal, Spit Point, and a point intervening between Horse Sand and Portsea Island. But after much discussion and numerous alterations of plan, it was only in 1864 that it was determined to proceed with the foundations at least of two—the Horse and the Noman forts. The foundation of eacli fort consists of rings of stone-work, laid on the leveled bed of the shoal, tapering a little upwards from a width of 54feet to one of 43 feet; the outer diameter of the ring gradually lessening from 231 to 213 feet. From 20 to 15 feet of sub-marine masonry is required. Outside the rings of stone are layers of rubble, to protect the stone-work from the action of tidal rush. Two years later, similar forts were begun on SpitBank and St. Helens shoal. In 1865 a mortar batterjr had been erected at Puckpool in the Isle of Wight, commanding at long range the approach to Spithead-In 1868, after it had been found impossible to secure a foundation for a fifth fort on the Sturbridge shoal. Puckpool Battery was strengthened and armed with 30 mortars and four 25-ton guns.

All this time the government had not determined which of three modes to adopt for constructing the forts—whether to form them entirely of iron; or of granite faced with iron; or simply of granite, leaving the facing for after-consideration. The plan most in favor with the government in 1866 was to erect on each of the foundations at Spithead a revolving iron fort or tower of enormous magnitude.

Circumstances in 1867 induced the government again to pause. Experiments on the Hodman 15-inch and 20-inch guns led some engineers to believe that no iron casing for forts could resist shot of 500 Ibs. to 1100 Ibs. from such ordnance; while the rolling of an armor plate 15 inches thick (see ARMOR-PLATES) revived the hopes of those who believe that armor will eventually vanquish guns. Finally, the forts are nearly finished, of a granite core, surrounded by a great thickness of iron plates. Above each fort are revolving turrets carrying 35-ton guns, which throw shells of 700 Ibs. The inner line of defence has been strengthened by new works at Gilkicker, Southsea Castle, &c., and by the increase in the size of the guns, and the additon of iron shields in the embrasures.