[5] Major Burr Porter of New Jersey,[6] a regular officer who had served on Fremont's staff was appointed commander of the regiment and promoted to colonel.
In response to Lt. Gen. Longstreet's Siege of Suffolk, The 2nd Brigade was detached on 15 April 1863, from XXII Corps and sailed down the Potomac to Hampton Roads as part of the relief force.
After Longstreet lifted the siege to rejoin Lee, the 40th moved across the James to Newport News where it remained for the remainder of May.
[7] Remaining in the Tidewater Virginia during the Gettysburg campaign, the regiment and the corps skirmished regularly with rebel forces keeping it under observation.
[10] It went up the beach to the trenches in front of Fort Wagner on 15 August where the regiment remained until the attrition inflicted on the defenders forced them out on the night of 6 September.
During Seymour's expedition, the Light Brigade's duties were the usual of a cavalry force with the added weight of a battery and infantry command.
On 15 February, a detachment of the 40th captured Gainesville for several hours and brought away a large amount of war supplies before rejoining the Union forces.
During the defeat at the Battle of Olustee the Light Brigade protected both Union flanks and screened the force on its retreat to Jacksonville.
[13] Arriving back in the Yorktown area 28 March 1864, the regiment turned in its horses and cavalry equipment and reverted to infantry.
As the Siege of Petersburg commenced, XVIII Corps as part of the Army of the James took up the left, southern wing of the Union forces.
Through its time in the siege, the regiment suffered many losses so that when it came out of line at the end of the Battle of the Crater, on 27 August, only two officers and forty-five men could muster.