The weeks that followed were spent by the _Cairo’s_ crew in gunnery practice and in patrolling the river above and below Memphis in an effort to break up the smuggling which was so evident at that point. They did an effective job. Meanwhile, Selfridge received notice from Porter that an active campaign on the Mississippi was about to begin. The campaign was to be another advance on Vicksburg, this time by land as well as by water. The Army of the Tennessee under General Grant was already moving southward from Tennessee. These troops, according to plan, were to advance by way of Grenada, down the corridor between the Yazoo and Big Black Rivers, and cut the Confederates off from their base of operations at Jackson. The Navy was expected to clear the Yazoo of the enemy as far up as Greenwood, where the light-drafts would turn into the Balobusha and ascend it to Grenada, and there destroy the railroad bridges. An attempt would also be made to capture the large number of steamers the Confederates had secreted in the twisting waterways of the Delta. Porter, on November 22, ordered Selfridge to bring his vessel to Helena. Three days later the _Cairo’s_ commander sent word that he had been asked by the Army to remain at Memphis and that he thought he would be doing right to fulfill the request. This brought a reply from Porter that was couched in sarcasm: “I would feel better satisfied to dispose of the vessels under my command as it seems best to me.” He said he would send a replacement for the _Cairo_, which was needed on the expedition he was planning. While awaiting the replacement, Selfridge continued to strengthen the _Cairo_. More railroad iron was added to reinforce the casemate protecting the boilers and machinery. His relief arrived on the morning of December 4, and he set out for the mouth of the Yazoo immediately, arriving on the 8th. The fleet that gathered there ready to go upstream was under the command of Capt. Henry Walke, a Mexican War veteran, a fine artist, and a dauntless fighter. The next 2 days were spent in recoaling. Then, on the 11th, plans for a reconnaissance up the Yazoo were carried out. This was done by the two tinclads, _Marmora_ and _Signal_, light-draft stern-wheelers covered with 1¼ inches of iron that afforded protection against shells but not against heavier projectiles. They ran up the river some 20 miles and prepared to round to, as the lookouts sighted several suspicious objects floating on the water. A man on board the _Marmora_ fired a musket at one of them and touched off a tremendous explosion that shook the boat and threw water over a wide area. Another explosion occurred shortly afterward near the _Signal_. No damage was caused by either. However, it was recognized that contact had been made with some of the vaunted Confederate mines, more commonly referred to as “torpedoes.”