The time was now close at hand when the weary and anxious waiting, which the admiral afterward so feelingly described, was to be exchanged for the more vigorous action he had so long desired. The co-operation of a division from Canby's army was assured toward the end of July; and at the same time the long-promised, long-delayed monitor ironclads began to arrive. As the want of these and the presence of the enemy's ironclads had been the reasons which, in Farragut's opinion, had made necessary the postponement of the purely naval part of the combined operation, a short description of the vessels which formed so potent an element in his calculations will not be out of place. The idea of the monitor type of ironclads, which was then the prevalent one in the United States Navy, was brought by John Ericsson from his home in Sweden, where it had been suggested to him by the sight of the rafts with a house upon them crossing the waters with which he was familiar. In its conception, the monitor was simply a round fort, heavily plated with iron, resting upon a raft nearly flush with the water, and provided with the motive power of steam. The forts, or turrets, as they are commonly called, might be one or more in number; and each carried usually two heavy guns, standing side by side and pointing in exactly the same direction, so that if discharged together the projectiles would follow parallel courses. Within the turret the guns could be turned neither to the right nor to the left; if such a change of aim were wished, the turret itself was revolved by steam machinery provided for the purpose. When loading, the port through which the gun was fired was turned away from the enemy; so that if a shot happened to strike at that time it fell on the solid armor. Above the gun-turret there was a second of much smaller diameter, which did not revolve. It was also heavily plated and designed to shelter the commanding officer and those charged with the steering of the ship. So much inconvenience was, however, experienced from smoke and from concussion when these steering turrets were struck, and their dimensions were so contracted, that many captains preferred to remain outside, where they could see better, their orders being transmitted to the helmsmen through the sight-holes pierced in the armor. Of these ironclads, four accompanied Farragut in his attack upon Mobile Bay. Two, the Tecumseh and Manhattan, came from the Atlantic coast, and were sea-going monitors. They had each but one turret, in which they carried two fifteen-inch guns, the heaviest then in use afloat. The other two were river monitors, built at St. Louis for service in the Mississippi. They were consequently of light draught, so much so that to obtain the necessary motive power they each had four screw propellers of small diameter, and they carried four eleven-inch guns in two turrets. Their names were the Winnebago and the Chickasaw. The armor of the two