Organized at Detroit in Aug. 1862, leaving the State on December 4th with 1,144 officers and men. Proceeding directly to Washington it joined the Michigan Brigade, then being formed, composed of the Fifth, Sixth and Seventh Michigan Cavalry, to which the First Michigan Cavalry was subsequently added. General Custer assumed command of the brigade while on its march to Gettysburg, where it had its first opportunity to distinguish itself under fire. The brigade sustained the heaviest loss at Gettysburg of any cavalry brigade in that battle. The Fifth was commanded there by Colonel Alger, who had served previously as a Major in the Second Michigan Cavalry, from which he was promoted to the Lieutenant-Colonelcy of the Sixth, and thence to the Colonelcy of the Fifth; he was one of the ablest cavalry officers in the Army. The loss of the Fifth at Gettysburg was 8 killed, 30 wounded, and 18 missing; Major Noah H. Ferry was killed there. At Hawes's Shop, out of 151 engaged, 55 were killed or wounded. The regiment met its heaviest loss in the cavalry affair at Trevilian Station, where in addition to the killed and wounded 136 Were taken prisoners,— the regiment having charged too far through an opening in the enemy's line, and being cut off from the brigade it was obliged to cut its way out.

Col. R. B. Price, Second Pennsylvania Cavalry, commanding brigade, will send forward all the available cavalry, with the Fifth Michigan Cavalry, on an expedition to thoroughly scour the country in our front as far as the Blue Ridge; and take a look across into the valley of the Shenandoah. He will particularly examine the gaps, commencing at Snicker's, as far as Manassas Gap, one column passing through Leesburg.

Yesterday I sent the Fifth Michigan Cavalry to occupy Snicker's Gap. I received a note from the commanding officer of the regiment last night, informing me that after a brisk fight he had taken possession of the Gap, with a loss of 2 wounded. We captured about 12 of the enemy, belonging to Jones' brigade. All is quiet to-day, with the exception of some little bushwhacking. Mosby is reported at Aldie.

Battery M, Second U.S. Artillery, under command of Lieutenant Pennington, was soon unlimbered and succeeded in shelling the enemy out of the woods on the right of the town. At the same time, Colonel Alger, of the Fifth Michigan Cavalry, who held the extreme left of my line, moved forward with one battalion of his regiment under the gallant Major Clark, and charged the enemy's battery. The charge, although daring in the extreme, failed for want of sufficient support. It was successful so far, however, as to compel the enemy to shift the position of his battery to a more retired point. Night setting in prevented us from improving the advantages we had gained.

Major Clark, Fifth Michigan Cavalry, was detached from his regiment with one battalion. When the command retired to the north bank of Broad Run, he, with a small portion of his battalion, became separated from the rest of the command and were captured by the enemy.