The fifteen inch pneumatic projectile, which
I described as being capable of sinking an armorclad at forty-seven
feet from where it struck, would have been capable of penetrating
fifty feet of cement had it struck upon a fortification. It was not
only a much larger quantity of high explosive than Europeans have
experimented with, but the explosive itself is probably more than
twice as strong as their gun-cotton and five or six times as strong as
their melenite. In the plans of Gen. Brialmont, one of the most
eminent of European engineers, he allows in his fortifications about
ten feet of cement over casements, magazines, etc. It is evident that
this is insufficient for dynamite shells such as I have described.
At Fort Wagner, a sand work built during our war, Gen. Gillmore
estimated that he threw one pound of metal for every 3.27 pounds of
sand removed. He fired over 122,230 pounds of metal, and one night's
work would have repaired the damage. The new fifteen inch pneumatic
shell will contain 600 pounds of blasting gelatine, and judging from
the German experiments at Kummsdorf, which I have cited, one of these
fifteen inch shells would throw out a prodigious quantity of sand;
either 500 pounds to one of shell, or 2,000 pounds to one of shell,
according as the estimate of Gen.
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