Smith was commissioned the colonel of the Third Vermont on July 23, 1861, but dated from April 27, making him the ranking officer of Vermont troops. On August 13, 1861, he was appointed a
brigadier general in the Union Army after helping organize the
1st Vermont Brigade. He was appointed a
brevet lieutenant colonel in the
regular army for his gallantry at the
Battle of White Oak Swamp in the
Seven Days Battles. On July 4, 1862, he received promotion to the rank of
major general in the Union Army. Smith led his division with conspicuous valor during the
Battle of Antietam, and was again brevetted in the regular army. When his corps commander, Maj. Gen.
William B. Franklin, was reassigned to a superior command, Smith was placed at the head of the
VI Corps of the
Army of the Potomac, which he led at the disastrous
Battle of Fredericksburg. The recriminations that followed Fredericksburg led to a famous general order in which army commander Maj. Gen.
Ambrose Burnside proposed to dismiss several of the senior officers of the army.
President Abraham Lincoln prevented this order from taking effect and relieved Burnside of his command instead. Smith was one of the affected officers, but it is to his credit that he did not leave the Army. However, his indiscretion in communicating to Lincoln directly about Burnside's shortcomings, compounded by the fact that Smith was a close friend of out-of-favor Maj. Gen.
George B. McClellan, resulted in his losing both his corps command and his rank; the Senate failed to confirm his nomination to major general, which expired on March 4, 1863. Reverting to the rank of brigadier general, he commanded a division-sized force of
militia within the
Department of the Susquehanna in
Pennsylvania during the critical days of the
Gettysburg campaign, repelling Maj. Gen.
J.E.B. Stuart at a
skirmish in Carlisle. Smith's green troops then participated in the unsuccessful pursuit of
Gen. Robert E. Lee back to the
Potomac River. He followed this in division command in
West Virginia. On October 3, 1863, Smith was assigned to duty as chief engineer of the
Army of the Cumberland (and a couple of weeks later, the
Military Division of the Mississippi). As such he conducted the engineer operations and launched the
Battle of Brown's Ferry, which opened the "Cracker Line" to provide supplies and reinforcements to the besieged troops in
Chattanooga. Of this action the
House Committee on Military Affairs reported in 1865 that "as a subordinate, General WF Smith had saved the Army of the Cumberland from capture, and afterwards directed it to victory." Smith was then renominated for the rank of major general of volunteers.
Ulysses S. Grant, who was much impressed with Smith's work, insisted strongly that the nomination should be confirmed, which was accordingly done by the Senate on March 9, 1864. Grant, according to his own statement "was not long in finding out that the objections to Smith's promotion were well grounded," but he never said what the grounds were, while Smith, contributing to a major series of war memoirs, maintained that they were purely of a personal character. For the
Overland Campaign of 1864, Smith was assigned by Grant to command the
XVIII Corps in Maj. Gen.
Benjamin Butler's
Army of the James, which he led in the
Battle of Cold Harbor and the first operations against
Petersburg. Smith's corps and a division of
black troops (under
Edward W. Hinks) were ordered to take the city. Remembering the debacle at Cold Harbor, Smith performed exhaustive reconnaissance. Determining that the section of the defensive line was manned primarily by artillery, he ordered an attack. The attack was successful in capturing several Confederate batteries and over a mile of entrenchments. However, by the time this was accomplished, Smith determined that darkness prevented him from effectively moving further. Both the time it took to prepare for the attack and suspending the attack at night has led some historians to see the outcome of the battle as a missed opportunity to shorten the war by nearly a year. But the fault may also lay with General Grant who failed to communicate with Smith, Major General George Gordon Meade and Major General Winfield Scott Hancock the full picture of the battle's true objective and provide the time to develop an effective operational plan. Smith's personal and professional differences with Generals Butler and Meade led General Grant to relieve Smith from command of the XVIII Corps on July 19, 1864. Smith spent the remainder of the war serving on military commissions, including one that discovered significant corruption in the Department of the Gulf. ==Postbellum career==