 She supplied ships at the mouths of the White and Arkansas Rivers with ammunition and ordnance, and occasionally fired at Confederate batteries ashore in the almost daily engagements in keeping open the far-spreading river highway system by which the Union divided and destroyed the South.While with the Mortar Flotilla 30 July 1862 she fired on cavalry attacking the boats near the mouth of the Arkansas River and succeeded in driving them off.During 1862 and the first half of 1863, the overriding concern of Union forces was the capture of Vicksburg, and "Great Western" spent much of her time during this period near the mouth of the Yazoo River above the city in support of combined operations there.