This study investigates the decisive factors that affected the Chickasaw Bayou Campaign, General Ulysses S. Grant's first effort to seize Vicksburg. By December 1862 Grant's forces had fought into north central Mississippi. Simultaneously, Major General John A. McClernand had convinced President Lincoln to allow him to command an independent amphibious force to operate on the Mississippi against Vicksburg. Grant hastily organized his own river expedition under Major General William T. Sherman to seize Vicksburg. The resulting campaign ended in the repulse of Union forces at Chickasaw Bayou. This study identifies the decisive factors at the strategic, operational, and tactical levels of war which contributed to the Union loss. Grant concluded from the campaign that fixed lines of communications were unnecessary in supplying his army. The Confederates were lulled into a false sense of security which ultimately contributed to their defeat at Vicksburg.