5. The service of the mortar by the artillerist has much to do with the wear of platforms.
NOTE Numbers 12.
IRON EMBRASURE LININGS. (See Figs. 20, 21, and 22, p. 321.)
Gabions, fascines, and hurdle work, when used for rivetting the cheeks of embrasures, were found to leak the fine dry sand used in the construction of our works, unless filled or backed with sand-bags. This remedy adds to the expense and labor, and is, besides, not very durable. Sods suitable for rivetting are very scarce on this coast.
Sand-bags alone lasted a long time in Battery Hays, but its guns were fired at an elevation of 5^ and upward. These high elevations gave a far less injurious cone of blast than low ones. The raw hides used for lining sand-bag embrasures were soon blown out (particularly by the Wiard gun), in spite of our efforts to make them fast by means of notched pickets.
To overcome these difficulties, a boiler or sheet-iron casing or lining was made from iron plates obtained from the wreck of an iron ship (a blockade-runner) which came ashore at Light-House Inlet. The splay, the dimensions of the throat, size of cheeks, length and inclination of sole, and thickness of plates used, were varied to suit the case. For direct firing, the splay may be 25^, or even less.
To set the casing, the genouillere is first finished, and the sole of the embrasure given its proper slope. On this sole is placed the iron casing, its directrix having the proper direction. Sand-bag merlons were built on each side, to which the lining was anchored by means of wires and crooked iron rods which were made fast to its cheeks and rings.
The plates used for the embrasure casing of gun Numbers 1, Battery Rosecrans (a 100-pounder Parrott rifle fired at Sumter with an elevation of 9^ 35'), were one-fourth of an inch thick, and weighed 10.4 pounds per square foot, corresponding with Numbers 3, Birmingham wire gauge. This was the heaviest iron employed. Of the eight embrasure casings in the second parallel, the above mentioned was the only one used against Sumter, and the only one supplied with a mantelet. This mantelet is of bullet-proof iron plate, arranged as a hanging door, which closes the throat of the embrasure. In this door is a cut or slot for the double purpose of allowing the reamer and sponge staves to pass through when loading, and for sighting the pieces. A small scantling of hard wood, with a rope attached to its upper end, is made fast to one side of the door, and acts as a lever to raise the door when the gun is fired. The swing bar of 1-inch round iron, upon which the hinges of the door are hung, has a collar at each end, to enable the cheeks of the carriage to resist lateral pressure. The sole was given a counter slope of 5^. The wings prevent the casing from being carried out by the force of the blast.
The cheeks are fastened to the soles and the wings to the cheeks by being riveted to angle iron.
The satisfactory results obtained from the use of these casings indicates that sheet and boiler iron should form part of the siege material furnished for military operations in a sandy country. If thick enough, it answers well for mantelets. All plates of this kind are easily converted into Sibley stoves for the use of an army in winter quarters.