Union Gen. Ulysses S. Grant, intent on keeping up the pressure on the enemy in the winter of 1863, dispatched a combined Army-Navy expedition to cross swampy, difficult terrain along the Yazoo River to flank Confederates defending Vicksburg, Miss., a city on bluffs overlooking the Mississippi River.

Grant’s aim was to get behind the rebel defenders holding heavily fortified Vicksburg, a bastion that so far had repelled all Union attempts to be captured.

The expeditionary force, which would begin moving after a levee breach on the Mississippi River on Feb. 3, 1863, would struggle and slog for weeks across watery terrain behind enemy lines and ultimately fail in March. The flood plain where the rivers meet contained inhospitable swamps, marshes and areas of dense brush. The passage of a flotilla of Navy gunships also was slowed by trees and other obstacles felled across waterways by Confederate foes.

Ultimately, the expedition would prove inconclusive and Grant would have to devise other means of attacking and overpowering Vicksburg, then an indomitable Confederate bastion commanding a key stretch of the Mississippi River — the main waterway for trade through the nation’s midsection.

The Associated Press reports this month 150 years ago during the Civil War that steamers attempting to ply the Mississippi River near Vicksburg have to risk attacks by Confederate guerrillas and occasional shelling while plying the river.