As the expectation was to fight generally bows on, the forward end of the casemate carried iron armor two and a half inches thick, backed by twenty-four inches of oak. The rest of the casemate was not protected by armor, except abreast of the boilers and engines, where there were two and a half inches of iron, but without backing. The stern, therefore, was perfectly vulnerable, as were the sides forward and abaft the engines. The latter were high pressure, like those of all Western river-boats, and, though the boilers were dropped into the hold as far as possible, the light draught and easily pierced sides left the vessels exposed in action to the fearful chance of an exploded boiler. Over the casemate forward was a pilot-house of conical shape, built of heavy oak, and plated on the forward side with 2½-inch iron, on the after with 1½-inch. With guns, coal, and stores on board, the casemate deck came nearly down to the water, and the vessels drew from six to seven feet, the peculiar outline giving them no small resemblance to gigantic turtles wallowing slowly along in their native element. Below the water the form was that of a scow, the bottom being flat. Their burden was five hundred and twelve tons.
The armament was determined by the exigencies of the time, such guns as were available being picked up here and there and forwarded to Cairo. The army supplied thirty-five old 42-pounders, which were rifled, and so threw a 70-pound shell. These having lost the metal cut away for grooves, and not being banded, were called upon to endure the increased strain of firing rifled projectiles with actually less strength than had been allowed for the discharge of a round ball of about half the weight. Such make-shifts are characteristic of nations that do not prepare for war, and will doubtless occur again in the experience of our navy; fortunately, in this conflict, the enemy was as ill-provided as ourselves. Several of these guns burst; their crews could be seen eyeing them distrustfully at every fire, and when at last they were replaced by sounder weapons, many were not turned into store, but thrown, with a sigh of relief, into the waters of the Mississippi. The remainder of the armament was made up by the navy with old-fashioned 32-pound and VIII-inch smooth-bore guns, fairly serviceable and reliable weapons. Each of these seven gunboats, when thus ready for service, carried four of the above-described rifles, six 32-pounders of 43 cwt., and three VIII-inch shell-guns; total, thirteen.