ain
ship channel to a red buoy, distant two hundred and twenty-six yards
from the water battery under Fort Morgan. This narrow passage, not
much exceeding one hundred yards from the beach, was left open for
blockade-runners, and through it the admiral intended his fleet to
pass; for the reports of refugees and the examinations made by
officers of the fleet who dared at night to push their search thus
close under the enemy's guns, alike affirmed that there at least no
torpedoes were.

The torpedoes planted in this part of the defences of Mobile were
principally of two kinds, both of the class known as floating
torpedoes. One was made of an ordinary barrel, lager-beer kegs being
preferred, pitched inside and out and with wooden cones secured to the
two ends to keep it from tumbling over. The barrel was filled with
powder and furnished with several, generally five, sensitive primers,
placed near together in that part of the bilge which was to float
uppermost. The primers were exploded by a vessel striking them and
communicated their flame to the charge. The other torpedo was made of
tin, in the form of a truncated cone, the upper diameter being the
greater. It was divided into two parts, the upper being an
air-chamber and the lower containing the charge. On top was a
cast-iron cap so secured that a slight blow, like that from a passing
vessel, would knock it off. The cap was fast to a trigger, and as it
fell, its weight pulled the trigger and exploded the charge. In July,
1864, there were planted forty-six of the former and one hundred and
thirty-four of the latter kind. Besides these which exploded on
contact there are said to have been several electrical torpedoes.

The first six months of 1864 wore away in the monotonous routine of
the blockade, broken only by an attack upon Fort Powell, made from
Mississippi Sound by the admiral with the light-draught vessels. These
could not get nearer than four thousand yards, but at the time,
February 28th, Sherman was on his raid into Mississippi and the attack
was believed to be of service as a diversion. During this half of the
year none but wooden vessels lay before Mobile. Toward the end of July
the co-operation of Canby's forces was assured and the monitor
ironclads began to arrive.

The root idea from which the monitor type of ironclads grew was a raft
carrying a fort; their hulls, therefore, floated low in the water, the
deck being but a foot or two above it. Upon the de