Y is For The Seige of Yorktown

"Having built the Army of the Potomac the previous summer, Major General George B. McClellan began planning his advance on Richmond for the spring of 1862. To capture the Confederate capital, he intended to move his army down the Chesapeake Bay to Union-held Fortress Monroe. From there, it would advance up the Peninsula between the York and James Rivers to Richmond. Such a move would allow him to flank and avoid Confederate forces in northern Virginia. It was his intention that US Navy warships would ascend both rivers to aid in expediting the advance. This element of the plan was thwarted in early March 1862 when the Confederate ironclad CSS Virginia attacked Union naval forces at the Battle of Hampton Roads. Though the threat of Virginia was mitigated by the arrival of the ironclad USS Monitor, efforts to contain the Confederate vessel drew off Union warships.  Despite this, McClellan pressed forward and his forces began landing on the Peninsula in mid-March. The Union advance was opposed by around 11,000-13,000 Confederates led by Major General John B. Magruder. Establishing himself near the old American Revolution battlefield at Yorktown, Magruder constructed a defensive line running south along the Warwick River and ending at Mulberry Point. Though a formidable barrier, Magruder lacked sufficient men to man the length of the Warwick Line. Assembling over 120,000 men, McClellan began advancing up the Peninsula. Locating Magruder near Yorktown, McClellan intended to hold him in place with Major General Samuel Heintzelman's III Corps while Brigadier General Erasmus Keyes' IV Corps moved south and west to cut off the enemy's line of retreat. The Union commander initially believed that the Confederate fortifications were limited to the vicinity of Yorktown. On April 4, Union forces pushed back Confederate skirmishers before encountering the Warwick Line the next day. Arriving at Lee's Mills, Keyes was surprised to encounter defenses manned by Major General Lafayette McLaw's division. Though he probed the enemy lines, Keyes did not press the attack and instead engaged the Confederates with his artillery.  The next day, Union troops led by Brigadier General Winfield Scott Hancock reconnoitered the Confederate lines north of Lee's Mill at Dam Number One. Taking some prisoners, Hancock reported that the enemy's defenses in the area were weak. Though alerted to this, McClellan took no action. This was largely due to his ill-informed belief that Magruder possessed over 40,000 men. Aware that he was badly outnumbered, the Confederate leader had worked tirelessly through various ruses to convince the Union leadership that his command was in fact larger. He accomplished this by marching a small number of troops past the same exposed location several times, frequently shifting his artillery, and laying down heavy fire whenever Union troops were sighted. These efforts were aided by a report from Keyes in which he informed McClellan that he did not think the enemy line could be taken.  Electing not to further scout the Confederate lines, McClellan stunned his officers and the enemy when he entrenched and laid siege to Yorktown. For the next week and a half, the Army of the Potomac dug in and began constructing a vast network of batteries. As the Union troops worked, Magruder was slowly reinforced to around 35,000 men. Building fifteen batteries, McClellan planned to emplace seventy heavy guns, including two 200-pdr Parrott Rifles, as well as over forty mortars. To aid in scouting the Confederate positions, Professor Thaddeus S. C. Lowe's Union Army Balloon Corps began flights over the lines using two balloons, Intrepid and Constitution.  Early on April 16, Union troops under Hancock again probed the area around Dam Number One. After his men briefly exchanged fire with the enemy, Magruder recognized the area's weakness and directed Brigadier General Howell Cobb to reinforce the area with six regiments. Receiving word that the Confederates were improving their lines, McClellan ordered Brigadier General William "Baldy" Smith's division to disrupt the enemy's work but not bring on a general engagement. Opening with an artillery bombardment, Smith later pushed forward Brigadier General William Brooks' Vermont Brigade. Crossing the dam, the Vermont men penetrated the Confederate lines before encountering Cobb's men. Fending off Confederate counterattacks, Brooks' men were ultimately forced to fall back when no reinforcements arrived to exploit their advance. Later in the day, Smith attacked further downstream but with no success.  As April progressed, McClellan continued work on his batteries. Across the lines, Confederate forces swelled to around 57,000 men and leadership passed to General Joseph E. Johnston. Aware that McClellan intended to begin an intense bombardment of his lines in early May, the Confederate leader made preparations for falling back towards Richmond. Though intelligence sources indicated that a Confederate withdrawal was pending, McClellan did not alter his plans which called for the bombardment to commence on May 5. In an effort to mask his intentions, Johnston bombarded the Union lines on the night of May 3. After dark, his army began retreating west. Ascending in one of Lowe's balloons the next morning, Heintzelman was stunned to find the Confederate trenches empty.  During the fighting along the Warwick Line, Union forces suffered 182 casualties while the Confederates incurred 300. Dispatching Brigadier General George Stoneman's cavalry to pursue Johnston, McClellan began organizing his infantry to advance. He also directed Brigadier General William Franklin's division to re-board their transports for a thrust up the York River. The two armies would next clash on May 5 at the Battle of Williamsburg. Though technically a Union victory, the Siege of Yorktown first showed McClellan's weaknesses as a leader. Overly cautious and paranoid regarding enemy strength, he would be repeatedly beaten on the Peninsula by General Robert E. Lee that summer."