PENETRATION OF IRON PLATES BY STEEL SUOT. 43J 



feet ; we can therefore find what thickness of unbacked plate it would liave 

 penetrated. 



From equation (2), 



'=V^ 



?>=6-76 inches. 

 And as the armour plating of the target was 4-5 inches, the backing, inclu- 

 ding the inner skin, was equivalent to an extra 2-20 inches of platiug. We 

 can also determine the "work" necessary to penetrate the -i-S-inch plate 

 (unbacked) by the above shot. From equation (1), 



5^'=27rIUi- = 608-4 foot-tons, 



or 28 foot-tons per inch of shot's cii'cumference. 



As the total force required to penetrate the target would be 01 foot-tons 

 per inch, we see that this may be divided into twenty-eight for the armour 

 plate, and thirtj--three for the backing. 



It is, however, possible that this backing might be penetrated with greater 

 ease if it depended on itself alone ; and possibly it is only when combined 

 with the armour plate that its resistance is so great*. 



That this reasoning is approximately correct, we find by examining the 

 results of round 979. 



Here the striking-" work " was 22 foot-tons per inch, and, as might be 

 expected, the plate was not penetrated ; again, round 736 struck with 39 

 tons per inch, and penetrated the plate, driving the pieces into the backing. 



We learn from the foregoing results that any good hemispherical-headed 

 steel shot will penetrate a structure like the ' Warrior,' provided the strildng- 

 " work " bo not less than about 61 foot-tons per inch of shot's circumference, 

 and that the shot hits direct t. 



In the absence of direct proof to tlie contrary, we may assume that the 

 same results would take place in the case of the ' Minotaur ' and ships of her 

 class. 



If we examine the results of round 1 in the Portsmouth experiments, it 

 appears that a spherical steel shot of 113-81 lbs. weight and 9-15 inches dia- 

 meter, monng with a velocity of 1450 feet, and consequent " work " of 57'7 

 foot-tons per inch, penetrated a o-o-inch plate and the side of a wooden fri- 

 gate, viz. 25 inches of wood. 



The amoimt of " work " due to the plate was here 41'4 foot-tons per inch, 

 which leaves 16-3 tons for the backing. 



It will be seen from this that the backing and inner skin of an iron-built 

 ship like the ' Warrior ' is capable of much greater resistance than the side of 

 an ordinary frigate. 



If we suppose the ship to have been protected with the 4-5-inch armour 

 plates, as in the case of " Portsmouth C " target, the resistance wiU be ap- 

 proximately proportioned to the squares of the thicknesses of the plates, the 

 backing being the same in both cases. 



We might therefore expect that a " work " of about 44 tons per inch 

 would penetrate " Portsmouth C." It appears from round 4 that 38-7 foot- 

 tons per inch failed to penetrate this target. 



* We have no experimental data to determine this point. 



t The above only ajjplies to hemispherical-headed shot ; if the projectile be cival- 

 hcadetl the " work" required will be less. 



