IRON-CLAD SHIPS 385 of resistance, and that no amount of strength- ening can compensate for the defects of the laminated system. The resistance of single ar- mor plates, shown by direct experiment for all thicknesses up to 5j in. to vary as the square of the thickness, does not obtain in laminated armor. For example, a 4-inch solid pluto would be 16 times as strong as a 1-inch plate, but would not be four times as strong as four 1-inch plates riv- eted together, although it would be much stronger than the laminated struc- ture. Excluding the Roan- oke and New Ironsides and the river ironclads, which leaves only the Monitor class, the armor of the American ironclads may be briefly summarized as fol- lows : The original Monitor had her hull protected by five layers of 1-inch plate, diminishing first to 4 in. and then to 3 in. in thickness below the wa- ter line; her turret, as previously stated, was built of eight layers of 1-inch iron. The wood backing of the hull armor was .27 in. thick, bolted to |-inch iron skin plating. The Passaic class have armor of the same thick- ness as the first Monitor, but have 39 in. of wood backing. The Oanonicus class have five layers of 1-inch plates, supported by two ar- mor stringers let into 27 in. of wood backing; their turrets have 11 layers of 1-inch plates. The Miantonomoh and the Monadnock, which are wood-built, are protected much like the Oanonicus. The Puritan and the Dictator have six layers of 1-inch plates on their sides, with 42 in. of wood backing; their turrets are '15 in. thick, made up of two drums, with segments of wrought-iron hoops 5 in. thick placed between the drums, which are com- posed of layers of 1-inch plates. In the Kala- mazoo class the total thickness of hull ar- mor is 6 in., made up of two layers of 3-inch plates, backed by 30 in. of oak, still further strengthened near the water line with three armor stringers, 8 in. square, let into the back- ing, and only a few inches apart. This is by far the most formidable armor carried by any of the American monitors ; and while there are in some places 14 in. of iron, there is no part of it nearly so strong as it would be with that thickness in solid plates. The turrets of the , Kalamazoo are 15 in. thick, like those of the Dictator, but none of them have any backing or wood about them. The rapid diminution in thickness of armor on these vessels is a se- rions defect, leaving no ground for comparison with corresponding English ships. The Dic- tator, for instance, 2J ft. below the water line, has but two 1-inch plates, and at 3 ft. only one Fig. 9 shows a section of the Dictator's armor, with one of the English turreted ship Thun- derer. Though generally unfit for cruisers, the monitors are well adapted to coast and harbor Fio. 9. Sections of the Armor of the Thunderer and Dictator. defence. The present strength of the United States iron-clad navy is as follows : NAME. Bate. Gum. Tonnage. Aiax Fourth 2 650 Fourth 2 488 Amphitrite Third Fourth 4 2 874 650 Camanche Catekill Chickasaw Fourth Fourth Fourth Fourth 2 2 4 2 496 496 460 483 Second 10 2,127 Dictator Second 2 1,750 Etlah Hero Fourth Fourth 2 1 488 488 Iris Fourth Fourth 2 2 488 496 Kewaydtn Fourth Fourth 4 2 640 488 Koka Lehigh . Fourth Fourth 2 2 488 496 Mahopac Fourth Fourth 2 2 650 550 Second 4 2.12T Miantonomoh Third Fourth 4 1 1,226 488 Modoc Fourth 1 488 Monadnock Third Fourth 4 2 1,091 496 Nahant Fourth 2 496 Nan tucket Napa Fourth Fourth 2 1 496 488 Nausett Fourth 2 488 Nebraska Second 4 2,125 Niobe Fourth 2 488 Second 4 2,127 Otsego Fourth Fourth 1 2 488 498 Piscataqua Puritan Fourth Second 1 2 483 1,870 6 2,260 Saujpas Fourth Fourth 2 2 560 488 Fourth 2 4S8 Third 4 1,085 Umpqua Fourth Fourth 2 1 488 4S3 Winnebago Wyandotte Fourth Fourth 4 2 640 650 Fourth 2 483 Yuma Fourth 2 488
