On the 10th of March, 1862, after the return of the Army of the Potomac to Alexandria, following the evacuation of Manassas, two detachments, each of 3 officers and 6 men, equipped and supplied with extra stores, were ordered to report, the one in charge of Lieutenant J. B. Ludwick, Ninth Pennsylvania Reserve, Volunteer Corps, and acting signal officer, to Major General H. W. Halleck, then commanding the Department of the Mississippi at Saint Louis, the other in charge of Lieutenant E. H. Russell, Ninth Pennsylvania Reserve Volunteer Corps, and acting signal officer, to Major General B. F. Butler, commanding the Department of the Gulf.

The party reporting to General Halleck formed under the orders of that officer a class of 20 officers and 40 men. This party was instructed, equipped, and prepared to take the field. A detachment from it served at Fort Saint Charles, White River.

At the time the whole party was reported for duty in the field and for some weeks after the Army of the Mississippi lay before Corinth. The country was unfavorable for their operations, and it was, perhaps, not contemplated that that army was to move, or that there might be service on the banks of the Mississippi and the incurment rivers. The officers composing the party were ordered by the general commanding to rejoin their regiments, and the organization was thus on the 30th of June, 1862, broken up. The operations of the fall and winter of 1862 - '63 have made it necessary to repeat the labor of the past spring, and to instruct and form anew the party of the Mississippi Valley.

The detachment detailed for the Department of the Gulf reached, after many delays, the headquarters of General Butler after the capture of New Orleans. A party was organized and instructed for service in this department. It served successfully at the battle of Bayou La Fourche. It constitutes now a part of the corps serving under General N. P. Banks.

From the date of the first order, in August, 1861, a party of 8 officers and 16 men, commanded by Lieutenant W. W. Rowly, Twenty-eighth New York Volunteers, and acting signal officer, was left to serve with the forces under General Banks. During the fall and through the winter and until the advance of the force of that general into the valley of the Shenandoah, this party held stations of observation and communication on Maryland Heights, on the heights at Point of Rocks, on Sugar Loaf Mountain, at Poolesville, Md., and on the ridge at Seneca. The labors and the usefulness of this party elicited the thanks of the general under whom it served.

Early in February, 1862, a movement of the forces under General Hooker on the Lower Potomac was contemplated. They were, it was said, to cross the river for an advance upon the enemy. A detachment of 8 officers and 25 men, equipped and mounted, commanded by Lieutenant B. F. Fisher, Third Pennsylvania Reserve Volunteer Corps, and acting signal officer, reported to General Hooker for service in the expected engagement. The enemy abandoned their batteries before an attack was made, and the river was crossed without opposition. The party rejoined the main Army of the Potomac in Alexandria in April, and accompanied it to the Peninsula.

MOVEMENT OF THE CORPS TO ACCOMPANY THE ARMY.

In the early days of March, 1862, the improving condition of the roads indicating that a movement of the army would be soon practicable, the corps was mobilized.