Union Headquarters monuments 

The monument to the Second Corps of the Army of the Potomac is on Hancock Avenue (39.814465° N, 77.235204° W; Google map; Tour maps: Hancock Avenue at Ziegler’s Grove or Hancock Avenue at The Angle) A Headquarters Marker is on Pleasonton Avenue just north of the State of Pennsylvania monument. (39.808258° N, 77.23489° W); Tour map: Pleasonton Avenue)Monument to the 2nd Corps of the Army of the Potomac at Gettysburg

2nd Corps Headquarters Flag
The Second Corps flag is a blue swallowtail with the corps number in red.

The Second Corps was commanded at the Battle of Gettysburg by Major General Winfield Scott Hancock, whose monument is on Cemetery Hill. Hancock was temporarily given higher command during parts of the battle and was wounded in Pickett’s Charge, and during these times Brigadier General John Gibbon took command of the corps.

From the monument:

Army of the Potomac
Second Corps
Major General Winfield S. Hancock
Brigadier General John Gibbon

First Division Brigadier General John C. Caldwell
Second Division Brigadier General John Gibbon
Brigadier General William Harrow
Third Division Brigadier General Alexander Hays
Artillery Brigade Captain John G. Hazard

July 2. Arrived between 6 and 8 A. M. on Taneytown Road and went into position on Cemetery Ridge on right of 5th Corps and at the left of the cemetery relieving a part of 1st Corps. Caldwell’s Division on the left Gibbon in centre and Hays on the right of line from Cemetery Hill to Round Top. Between 5 and 6 P. M. Caldwell’s Division was sent to the support of 3d Corps and was engaged until sunset. It returned to its first position.

July 3. At 1 P. M. the Confederate artillery opened a heavy fire all along Hill’s Corps and the left of Longstreet’s Corps for two hours when an assault under the command of General Longstreet was made by a force of about 15,000 which was repulsed with great loss in killed wounded and prisoners.

Casualties Killed 66 Officers 731 Men Wounded 270 Officers 2924 Men Captured or Missing 10 Officers 365 Men Total 4369

Marker for the Second Corps headquarters of Union Major General Winfield Scott Hancock at Gettysburg

From the Headquarters Marker:

Army of the Potomac
2d Corps Headquarters
Major General Winfield S. Hancock,
July 1, 2, 3, 1863