HEADQUARTERS DEPARTMENT OF THE NORTHWEST,
Milwaukee, Wis., August 12, 1864.

Major General H. W. HALLECK,

Chief of Staff of the Army, Washington, D. C.:

GENERAL: I have the honor to acknowledge the receipt of your telegram of yesterday and to report as follows:

There are now in the Military District of Minnesota, which extends as far west as Devil's Lake and the line of the James River, six companies of the Second Minnesota Mounted Rangers, four companies of Hatch's Independent Battalion, and four companies Thirtieth Wisconsin Volunteer Infantry. The two first-named detachments are scattered about in small bodies from Fort Ripley to Fort Abercrombie, and thence to Fort Ridgely and the northern line of the State of Iowa, covering the frontier during the absence of the Indian expedition, as well as so small a force can do it. These detachments are nothing more than mounted rangers, mounted on small Canadian ponies, which were bought for service on the plains. Neither troops nor horses would be worth much, if anything, with any of our armies in the field. It would take twenty-five days to assemble these detachments at Saint Paul, the nearest point at which they could procure transportation south, and even then but a part of them could be sent, until relieved by other troops, without abandoning Forts Ripley, Abercrombie, and Ridgely. The number which could be assembled at Fort Snelling within twenty-five days would not exceed 300, and those badly mounted for anything but frontier service, and little serviceable for anything else. The four companies Thirtieth Wisconsin Infantry have just reached the point near James River and have begun to build Fort Wadsworth. They cannot be taken away, until relieved, without abandoning a large amount of public property and giving up the establishing the post is 340 miles northwest of Saint Paul, and to communicate with these and bring them back to Saint Paul, to which point they must march, would require six weeks at the least, even supposing the order to be sent at once and everything to be abandoned. These are all the troops fit for service in the District of Minnesota, and you will readily see that even if all were taken, without being relieved, they could not be assembled at Saint Paul much, if any, before October 1.

In General Sully's District of Iowa about two-thirds of all the forces in the department are now serving, all of whom, with the exception of one company Sixth Iowa Cavalry and one company of Dakota cavalry at Yankton, one company Seventh Iowa Cavalry at Vermillion River, detachments of three cavalry companies at Farm Island and two companies of Thirtieth Wisconsin Infantry at the same place, about seven companies in all, are with General Sully's expedition. These seven companies are posted so as to cover the frontier, as far as possible, during Sully's absence, and could not be taken away without creating an immediate stampede of the inhabitants. General Sully, after establishing the location of Fort Rice on the Missouri, above Cannon Ball River, left four or five companies to build the post, and on the 18th of July marched with the remainder of his command for the Yellowstone, near which the combined Indian force was encamped. Fort Rice is 450 miles northwest of Sioux City and cannot be communicated with in less than twenty-five days. If boats were there ready the troops now at that post night be brought to Saint Louis (if the Missouri is navigable) in about twelve days more by abandoning the post and all public stores.