What we have are brick and stone casemates and earthworks. A sample granite
casemate, with iron-lined embrasure, was built at Fortress Monroe, and 8
shots were fired at it from a 12 in. rifle converted from an old 15 in.
smooth bore. This gun develops only 3,800 foot tons of energy--a mere
nothing compared with the 62,000 foot tons of the English and German 110
ton guns.

General Abbott showed most conclusive proof of the worthlessness of masonry
forts in pictures showing the effect of the shots. The massive 8 feet
thickness of granite was pierced and battered till it looked like a ruin.
Not a man inside would have been left alive.

He also showed a "disappearing" gun in an earthwork, the gun recoiling
below the level of the parapet and being run up to a firing position by a
counterweight. In 1878 Congress stopped all appropriations for defenses,
and nothing had been done since.

General Abbott said that we needed submarine mines or fixed torpedoes,
which should be thickly interspersed about the channel and be exploded by
an electric battery on shore. To prevent these torpedoes from being
exploded by the enemy, the surface over them should be covered by plenty of
guns. Heavy guns and mortars were needed to resist attacks by heavy
iron-clads. Movable torpedoes were valuable, but only as an auxiliary--a
very minor auxiliary--compared with submarine mines. We should be cautious
not to infer that torpedoes made a satisfactory defense alone, as they must
be protected by large and small guns, and they form only a part of the
chain of general defenses.

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