the battle of yorktown or siege of yorktown was fought from april 5 to may 4, 1862, as part of the peninsula campaign of the american civil war. marching from fort monroe, union major general george b. mcclellan's army of the potomac encountered maj. gen. john b. magruder's small confederate force at yorktown. mcclellan suspended his march up the virginia peninsula toward richmond and settled in for siege operations.