During the Civil War, the Union Navy and Army worked together to maintain control of the Mississippi River, which was a vital transportation route for the South. They also worked to capture key Confederate ports, which helped to cut off supplies and weaken the Southern economy. Additionally, they fought major battles in key locations that helped to turn the tide of the war in favor of the Union. Overall, the Union Navy and Army played a crucial role in maintaining control of the war and ultimately securing victory for the North.