HEADQUARTERS DEPARTMENT OF THE GULF,
ON BOARD U. S. STEAMER AVENGER,

Mississippi River, May 21, 1864. (Received 12 m., 27th.)

At the date of my dispatches, transmitted by General Hunter, orders had been given for the construction of a dam on the Red River above Alexandria, for the relief of the entire fleet of the navy, which was detained above the rapids. The dam was commenced on Monday, the 2nd of May, and was completed on Sunday, the 8th. This work was constructed under the direction of Lieutenant-Colonel Bailey, of the Fourth Wisconsin Volunteers, to whom it is impossible to accord too much praise for the skill and energy with which he pursued this work. The army gave its labor to the completion of the work, night and day, with the greatest spirit and success. Two of the gun-boats came over on Sunday evening, and on Monday morning, at 5 o'clock, a portion of the dam gave way, which reduced the water on the rapids to its original level. Its reconstruction was immediately commenced, and completed, with additional wing-dams above the rapids, on Thursday, the 12th, which raised the water to a sufficient height to allow the boats to pass; and on Thursday evening and Friday morning they all passed over the falls created by the dam in safety. The rapids extend in length 1 1/4 miles, making a gradual descent of 8 feet and some inches, and the fall occasioned by the water passing through an opening made in the dam for their final escape was 5 1/2 feet, making an entire fall of 13 1/2 feet. On the release of the gun-boats the army took up its line of march for Simsport. It encountered the enemy in full force on its march, on a prairie near Mansura, where it occupied a position covering three roads, leading to Cheneyville on the right, to Simsport on the left, [and to Moreauville,] over one of which the army must pass. A sharp engagement ensued, lasting about four hours, and chiefly confined to the artillery. Our troops getting possession of the wood in which the enemy was posted drove him back on the road to Moreauville. We pursued him upon the second road to Simsport, where it arrived on the morning of the 17th. The Atchafalaya was bridged by the use of the transport vessels, and the passage of the river was completed. On the evening of the 20th [18th?], General Mower's division of the Sixteenth Corps, supported by a brigade of cavalry of the Nineteenth Corps, had a sharp engagement on Yellow Bayou with the enemy, in which we captured 180 prisoners. Our loss in killed and wounded was 140. The enemy's force was estimated at 8,000. Throughout the entire campaign, except in killed and wounded (in which at Sabine Cross-Roads, Pleasant Hill, Mansura, Yellow Bayou, and other battles our losses have been severe), no prisoners, guns, wagons, or other material of the army have been captured by the enemy, except that abandoned to him in the unexpected engagement at Sabine Cross-Roads on the morning of the 8th of April. With the exception of the losses sustained there the material of the army is complete. General Canby arrived at Simsport on the 18th, and remained until the passage of the river was completed. The troops will rendezvous at Morganza, on the Mississippi, a point they reach to-day and to-morrow.

N. P. BANKS,

Major-General.

SECRETARY OF WAR.

13 R R - VOL XXXIV, PT I