The Battle of Dam #1 was part of the Peninsula campaign. Lincoln's plan was to split the Confederacy to disrupt supplies and reinforcements in an effort to force the Southern states to surrender. Jefferson Davis' strategy was one to cordone, counter the Union attacks in a defense of the entire perimeter of the Southern states; this proved to be an unmanageable burden and failure leading to the South's ultimate defeat.
Even by 1862 the War was becoming increasingly unpopular in the North with Copperhead Southern sympathizers and others suffering a worsening economy. Lincoln sought a bold offensive.
General McClellan assumed command of the US Army and considered two plans; the first, march directly to Richmond which was just 70 miles south of Washington DC but river crossings would make this approach very difficult. The second was to use the superior strength of the US Navy to move troops by sea down to the York and James Rivers and move inland from those landings to Petersburg and Richmond.
Confederate General John Magruder serving under General Johnston was sent to build entrenchments across the peninsula below Yorktown to deter such a Union advance. On March 17, 1862 Union troops under Gen. William "Baldy" Smith landed at Fort Monroe and marched inland. McClellan and Smith were using erroneous maps though which showed the position, orientation and flow of the region's rivers incorrectly. The Confederates lines were anchored along the river which varied between 10-60 feet wide. The Union troops believed the river could be easily bridged but the Confederates had dammed the river to make it deeper and wider including at Dam #1. Dam #1 was approximately 1000 yards across including emplacements. The Confederates also commanded a position along high ground on the north and west side of the river. They also built a gun fort overlooking the dam with a single 12 pound cannon as armament whereas the Union troops had more artillery - New York artillery units there possessed 10lb rifled parrott guns.
The 2nd Vermont Regiment with a total force numbering around 3000 attacked the Confederate positions with storming parties supported by artillery fire from the east bank of the river. The Confederate defenders, mostly troops from North Carolina and Louisiana numbered approximately 1800 troops. The Union forces sustained 198 fatalities while the Confederates lost 20 plus 41 wounded but, the Federals took the dam. But ultimately, the delay there at the Battle of Dam #1 allowed Confederate General Johnston time to reinforce his defenses around Richmond which led to an eventual Confederate victory in the Peninsula campaign.
Lessons learned from the Battle of Dam #1 included:
1) McClellan had poor intelligence including incorrect maps
2) Magruder made good use of terrain and deception including false timber cannon enplacements
3) Johnston was able to use delays to consolidate defensive units
4) This was the first battle of the war for many of the troops.