620 



NAVY, UNITED STATES. 



of 8 inches, was completely penetrated by 

 the 8-inch 68-pdr. smooth-bore gun and the 

 100-pdr. rifle, at 200 yds., though at like 

 range these guns have not greatly injured the 

 best 44-inch solid plates ; and a 10-inch tar- 

 get similarly constructed was much bulged and 

 broken at the back by the same guns. From 

 these and other data, Fairbairn deduces a con- 

 clusion in common with that now generally 

 held in England and France and made in 

 those countries the leading argument in favor 

 of armoring with single thick plates namely, 

 that up to a certain limit, and which lies be- 

 yond the thickness of any plates yet adopted, 

 the resistance of the plate to shot increases 

 very nearly as the square of the thickness ; so 

 that with thicknesses of 1, 2, 3, etc., the capaci- 

 ties of resistance are as, 1, 4, 9, etc. ; and that 

 a single 4^-inch plate has practically about 

 twice the strength of two 2J-mch plates laid 

 together, though the latter give the same total 

 depth of metal. In the experiments of Mr. Ste- 

 vens in 1854, however, a 10-inch 125-pdr. round 

 shot, with 10 Ibs. of powder, and having about 

 the same penetrating power with either of those 

 above named, only slightly indented and did not 

 break a 6|-inoh target composed of plates of 

 similar thickness to those made use of in the 

 English experiments. It is stated that the ex- 

 periments, individual and official, on the sub- 

 ject in this country concur in showing even a 

 superior resistance in laminated armor. The 

 comparatively smaller firing charge, and lower 

 velocity of ball which have here been hitherto 

 the rule, may serve in part to explain away the 

 value of these results. In explanation of the 

 assumed superior resistance of single thick 

 plates though the fact makes against them 

 when penetration actually occurs it has been 

 urged that in punching such a plate with a 

 projectile, the hole made is conical, about the 

 size of the ball in front, and much larger at 

 back, while the hole made through laminated 

 armor is cylindrical ; so that, in the former tho 

 sheared or fractured area must be much greater. 

 Besides the area of fracture, however, and 

 the absolute thickness of single or partial plates, 

 many other circumstances must enter to decide 

 in a given case the relative capacities of the 

 ball and the armor. Among these are : differ- 

 ences in the qualities of the metal of the ball 

 and of the armor, as in case of the best hard- 

 ened steel shot striking armor which has either 

 too great brittleness or too great softness ; the 

 presence or absence of uniform cohesion and 

 strength throughout the thickness of each single 

 or partial plate, depending on the manner in 

 which it has been manufactured ; the necessity 

 of joints and bolts or rivets in the armor al- 

 most always elements of weakness at the points 

 where they occur ; and the extent to which the 

 mode of applying and fastening the plates is 

 made to prevent or compensate such weakness. 

 The latest conclusions still appear to be to the 

 effect that, for the most effctive sort of plating, 

 the three qualities requisite are: 1, that the 



iron shall not be of a crystalline texture ; 2, 

 that it shall possess considerable ductility and 

 the greatest possible tenacity ; 3, that, to these 

 ends, it shall be a very fibrous iron. To these 

 qualities it will probably have to be added that, 

 fourthly, in order to effectual resistance to the 

 almost unfracturable shot of metal having the 

 utmost tenacity and hardness, the possession 

 also on the part of the plate of the utmost hard- 

 ness compatible with the three qualities above 

 named, is indispensable. Beside the use of 

 Franklinite, presently to be referred to, it has 

 been suggested that possibly a very low Bes- 

 semer steel, or iron, as likely to supply all the 

 needful conditions, may yet be cheaply adapted 

 to the making of armor plates. 



Mr. A. L. Holley, after remarking that our 

 information in respect to the relative strength 

 of single and laminated armor is still too in- 

 complete to warrant a conclusion, adds: " It is 

 probable that the heavy English machinery 

 produces better- worked thick plates than have 

 been tested in America, and that American 

 iron, which is well worked in the thin plate 

 \ised for laminated armor, is better than Eng- 

 lish iron ; while the comparatively high veloci- 

 ties of shot used in England are more trying to 

 thin plates, and the comparatively heavy shot 

 in America prove most destructive to solid 

 plates. So that there is as yet no common 

 ground of comparison [between the results ob- 

 tained in the practice of the two countries]." 

 In respect to joints and fastening, Fairbairn was 

 led by tests made with a view to this particu- 

 lar subject, to the result that, taking the co- 

 hesive strength of a given plate at 100. the 

 strength of an ordinary double-riveted joint is 

 about 70, and that of a single-riveted joint not 

 more than 56. 



It appears very recently to have occurred to 

 the English naval authorities that the bending 

 of the thick iron plates to fit the ship's sides, 

 as has so far been practised in case of all or 

 nearly all their armored vessels, must render 

 the plates so bent more vulnerable. Very few 

 of the American armored vessels have been 

 constructed with bent plates ; among such are 

 at least the Roanoke and the Onondaga. It 

 would seem that the greatest strength, in this 

 respect, would be secured by forging the plates 

 as nearly to the required shape as possible, and 

 then fitting the sides or backing to the plates, 

 rather than -these to the surface they rest upon. 



The Recent Experiments with Modern Heavy 

 Ordnance. In October, 1861, a target 20 feet 

 long by 10 feet wide, and representing the side 

 of the Warrior 4^- inches of solid iron on 18 

 inches of teak backing, with an inner lining of 

 |-inch wrought iron was fired on at 200 yards' 

 distance, at Shoeburyness, during the principal 

 part of two days, with solid 68-pounders, 110- 

 pounders, and 200-pounders, both singly, and 

 also in salvos of 3, 4, and 6 guns at a time, 

 concentrated on white spots painted on the 

 supposedly weaker parts of the target. The 

 missiles simply rebounded, or broke and flew 



