a plan to take Richmond by transporting his forces via steamship to Urbanna, Virginia and outflank the Confederate forces outside Washington. This became known as the Peninsular Campaign. Union forces maneuvered up the James River and disembarked at Harrison's Landing, then marching towards Richmond. The Union forces split at the Chickahominy River, with a smaller force on the southern side of the river. On May 31, Confederate General Joseph E. Johnston, firmly believing the city could not withstand a major siege, counterattacked. The following battle became known as the Battle of Seven Pines (or Battle of Fair Oakes). Although the result was inconclusive, the Confederates unknowingly managed to halt McClellan's march towards Richmond. Following the Battle of Seven Pines, the regiment was officially transferred to the Army of the Potomac, under General McClellan. The regiment was assigned to the 1st Brigade ("Robinson's Brigade"), of the 3rd Division (Kearney's Division), of the III Corps, commanded by General Samuel P. Heintzelman. Although the commanders of the Brigade, Division, and Corps changed throughout the war, the 20th was never reassigned. Battle of Oak Grove Coming nearly three weeks after the Battle of Seven Pines, the Battle of Oak Grove was McClellan's only offensive movement during the Peninsular Campaign. The action was meant to secure the Union left flank, so that McClellan could bring his siege guns into position just south of Old Tavern. The 20th Indiana was located on the left side of the advancing Union picket line. The regiment began advancing with the rest of the picket line at 8:30 A.M., and encountered mild resistance, with the majority of the fighting taking place on the far right flank of the Union line. McClellan ordered the advance to halt at 1 P.M., fearing that casualties would be too high. Upon surveying the field for himself, he allowed the advance to continue. During this pause, Confederate troops seized the opportunity to regroup, and at 5:30 P.M., launched a counterattack against the Union left flank, the location of the 20th Indiana. The 87th New York Regiment, which was in the immediate right of the 20th Indiana, broke under heavy pressure from the Confederate charge, just as the 20th was beginning a charge of its own against the confederate positions. This fully exposed the right flank of the 20th Indiana to the Confederate attack. Although the regiment initially fell back in "great confusion". Private Joshua Lewis