In the assault at Cold Harbor, June 1, 1864, the corps sustained another severe loss, 2,715 of its number killed or wounded. Accompanying the army to Petersburg, it participated in the preliminary operations incidental to the investment of that stronghold. But its stay was of short duration. Lt. Gen. Jubal A. Early's invasion of Maryland necessitated a transfer of troops to confront him, and the VI Corps selected for that duty in the Valley Campaigns of 1864. On July 6, Ricketts's (3rd) Division embarked at City Point, and, landing at Baltimore on July 8, marched out to meet Early. This division took part in the Battle of Monocacy on the following day, and, although unable to defeat Early, checked his advance on Washington, D.C., giving the defenses their time to organize. The other two divisions embarked on July 10 and, landing at Washington, attacked Early, whose advance had reached Fort Stevens, within the city limits. The brunt of this fight fell to the lot of Brig. Gen. Daniel D. Bidwell's (3rd) Brigade, of Getty's (2nd) Division, every regimental commandant in this brigade, but one, being either killed or wounded.