overthrowing the rebel authorities holding the semblance of Confederate power in that city, was commenced on the Rapidan in May, 1864. The battles of Todd's Tavern, on the 7th of May; of Spotsylvania, on the 14th and 19th, and passage of the North Anna, on the 24th; of Cold Harbor, on the 31st of May and 1st of June; the march thence and passage of the James River on the 16th, 17th, and 18th, with the investment of Petersburg on the 3rd of July, 1864, constitute a brilliant series of grand battles and maneuvers that do not come within the scope of engineer reports.

The annexed narrative and information from the report of Colonel Michler, dated October, 1865, give more specifically the labors of the officers of the Engineer Corps during the progress of this campaign.

SEA-COAST AND LAKE DEFENSES.

While most of the officers of the Corps of Engineers have been actively engaged in the field, as heretofore stated, others have given their attention to the important labor of sea-coast defenses.

Against predatory expeditions of rebel cruisers and iron-armored vessels, built in foreign ports claiming to be neutral, it was necessary to construct batteries to mount rifle artillery and smooth-bored ordnance of heavier calibers than heretofore used. Colonel Macomb, Major Blunt, Major Casey, of the Corps of Engineers, were employed in thus fortifying thirteen harbors on the Eastern coast. At the same time progress on the permanent sea-coast defenses was continued at all the harbors from Maine to Hampton Roads inclusive, at Key West and Tortugas, and as San Francisco; and repairing the permanent works on the Gulf of Mexico that were taken from the rebels, which had been more or less injured by them and by our attacks, to restore them to the Union. On the Northern and Eastern works, as also on the California coast, the main object has been so to direct the operations as soonest to mount the contemplated armaments, which, at this time, are required to be of such penetrating and crushing power as will in all probability insure the destruction of any iron-armored vessels that can combat them. The introduction of these increased calibers and this power of artillery has made it necessary to renew most of the gun platforms heretofore constructed, which were designed for no longer caliber than 42- pounders. At the present time no smaller gun is prepared for the sea-coast batteries than 100-pounder rifle guns, and ten to fifteen inch rifled and smooth-bored guns.

The further construction of the sea-coast batteries has been retarded by the necessity which now exists of so covering part of our guns and gunners as to render them secure against any advantage that an attacking power in iron-armored ships opposed to them shall possess. So far as we have yet progressed, preparations for guns of large caliber have been perfected, and the guns mounted to throw, collectively, 147,150 pounds of metal at a single discharge, which is an addition during the year of 40,651 pounds of metal that can be so thrown against an enemy.

Continuing to increase the armament on our sea-coast in the same ratio for a reasonable time will render the harbor defenses exceedingly difficult for any maritime power to overcome, and, in combination with other auxiliary means of defense, will carry the cost and time requisite to subdue them beyond the means of foreign powers, provided we hold our works in a perfect condition for both land and sea attacks.

Continuing to increase the armament on our sea-coast in the same ration for a reasonable time will render the harbor defenses exceedingly difficult for any maritime power to overcome, and, in combination with other auxiliary means of defense, will carry the cost and time require to subdue them beyond the means of foreign powers, provided we hold our works in a perfect condition for both land and sea attacks.