Dunham spent the winter of 1861–1862 encamped with the 11th Massachusetts near Washington while the Union army trained and prepared for the Peninsular Campaign. At the start of the campaign, the regiment was engaged in the Battle of Williamsburg on May 5, 1862, taking serious casualties. For their conduct during the battle, the Governor John Andrew of Massachusetts awarded the unit a new regimental battle flag. During the remainder of the Peninsular campaign, the 11th Massachusetts was primarily engaged in picket duty. They played a minor role in the Seven Days Battles being engaged in the Battles of Savage's Station and Malvern Hill.