Union Artillery and Pickett's Charge

A Geospatial Perspective

At 1:07pm on 3 July, 1863, the 150 massed guns of the Confederate States’ Army of Northern Virginia opened fire on Federal positions to their east, rending through the quiet Gettysburg afternoon. The barrage’s bellows could be heard as far away as Pittsburgh.¹ The rebel bombardment lasted approximately one hour, at which point James Longstreet gave the green light for George Pickett’s division to begin its assault on Cemetery Ridge.²

The Confederates were banking on the possibility that they had degraded the Army of the Potomac’s field artillery sufficiently to allow for successful exploitation by the infantry assault. It turned out that their cannon had aimed high.³

The ensuing bloodbath that Federal artillery inflicted on the 14,000 Confederate troops who attempted to cross that field is the most famous event in American military history. As the story of Southern infantrymen’s disintegration under blistering cannon fire has been told and retold, the history of the Union artillery response to Pickett’s Charge has been written mainly as a qualitative experience—the terror, the noise, the carnage.

Today, I’m doing something different. Using geospatial tools, I’ll be examining the quantitative influence that Union Chief of Artillery Henry Hunt’s Yankee cannon had in breaking Lee’s four divisions.

A major source for my project is this map, produced by David Shultz and Richard Rollins for an article in Gettysburg Magazine titled “Measuring Pickett’s Charge.” This depicts the positions of Federal artillery batteries on the afternoon of 3 July, with lines representing “slightly conservative” estimates for the ranges of individual cannon.⁴

Based on Shultz and Rollins’ map, I created a digital representation of the sectors of fire observed by Hunt’s artillery batteries, mapped against plausible routes of advance for the 50 rebel regiments that participated in Pickett’s Charge. The routes of advance are based on American Battlefield Trust researcher Steven Stanley’s documentation of Confederate positions during the Battle of Gettysburg

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Next, I compiled data on regimental casualties from 3 July (using John W. Busey and Travis W. Busey’s Confederate Casualties at Gettysburg: A Comprehensive Record) and did some analysis on the relationship between exposure to Union artillery and losses taken by Confederate regiments in Pickett’s Charge.

First, I measured this relationship cumulatively. To measure the cumulative impact of Union artillery on Confederate losses, I used the aggregated distance travelled by every regiment within range of each Union battery (for example, if one regiment travels one meter while in range of three different batteries, that would count as 3 meters), compared to the percentage of casualties each unit suffered on 3 July.

This linear regression indicates a pretty strong cumulative relationship between exposure to artillery fire and losses taken by Confederate forces. It makes sense intuitively—units travelling further in view of more Federal batteries tended to take heavier losses—but we have to consider the chaotic context from which this data originates. In a setting where artillery batteries are constrained by their firing rates, limited ammunition reserves, and inability to target more than one enemy unit at a time, and where the influence of the Union infantry’s defense, the friction of combat, timing, and a million other factors are disrupting both Union artillery and Confederate infantry, the strength of the relationship between total Confederate exposure to artillery fire and losses is remarkable.

Next, I measured for the relative relationship between artillery exposure and casualties by controlling for distance travelled. To do this, I created an Artillery Exposure Index, which is the aggregated distance travelled by every regiment within range of each Union battery divided by the total length of the regiment’s route, and the Relative Casualty Index, which is the percentage of losses taken per regiment on 3 July divided by the length of the regiment’s advance. One way to think of it is that the Artillery Exposure Index measures how “hot” each regiment’s route of advance was, while the Relative Casualty Index measures what percentage of losses each regiment took with each meter of its advance.

Measuring for the relative relationship between losses and exposure dilutes the stronger correlation seen in the cumulative measurement. While there remains a positive correlation between exposure to artillery and loss percentage, there is much more variation from regiment to regiment. This indicates that the intensity of artillery fire alone had a somewhat mixed impact on inflicting casualties, a result that squares with qualitative assessments of artillery at Pickett’s Charge, which suggest that while long-range artillery fires had significantly depleted rebel forces’ chance of success, it was close-quarters canister shot and Union infantrymen’s riflery which played the decisive role in repulsing the Army of Northern Virginia.⁵

My geospatial analysis suggests that the casualties suffered by rebel forces were more influenced by the length of the movement and distance travelled under fire than the relative severity of their exposure to Union artillery fire. When Robert E. Lee made the catastrophic decision to gamble the superior fighting spirit of his army against sheets of cast iron shot, it may have been the expanse of earth itself that damned him.

Map sources:

Terrain of battlefield based on map by Hal Jespersen, www.cwmaps.com

Confederate regiment positions based on map prepared by Steven Stanley from the Civil War Trust.

Road networks based on maps from the Atlas to Accompany Steele’s American Campaigns from the Library of Congress.

Federal fields of fire based on map by David Shultz and Richard Rollins, from their article “Measuring Pickett’s Charge.”

Author’s note⁶

1. McPherson, James M. 2003. Battle Cry of Freedom. N.p.: Oxford University Press, USA, 661.

2. Hess, Earl J., and Brendan Wolfe. n.d. “Map of Pickett's Charge.” Encyclopedia Virginia. Accessed July 3, 2025. https://encyclopediavirginia.org/entries/picketts-charge.

3. McPherson, Battle Cry of Freedom, 662.

4. Shultz, David, and Richard Rollins. n.d. “Measuring Pickett's Charge.” Gettysburg Magazine. http://www.gdg.org/Gettysburg%20Magazine/measure.html.

5. Hess, Earl J. 2001. Pickett's Charge--the Last Attack at Gettysburg. N.p.: University of North Carolina Press, 200.

6. I wanted to do a little post-lab breakdown, like we used to do in tenth-grade chemistry.

Casualty statistics, especially from the Civil War period, can be misleading, due to the intensity of friction in combat. There is significant anecdotal evidence that regiments in combat would hemorrhage troops (many of them not necessarily deserting out of fear or cowardice but simply getting lost in the mayhem), and this would disrupt any attempt at a clean statistical tallying of troops engaged in Pickett’s Charge and the troops lost in the course of the action. 35 of 50 of the Confederate regiments analyzed in this article had already been engaged in combat in the previous days, and tallies of the troops they would have brought into Pickett’s Charge may overcount because there is no record of the troops who may have gotten lost in previous actions and only rejoined the unit after the charge.

Additionally, the sample size for this project (50 regiments) is relatively small, which limits the potential for arriving at statistically significant conclusions. Pickett’s Charge has the advantage of being one of the most notorious and well-documented frontal infantry assaults in world history, which has made this study much more painless to conduct, but the focus on one attack can be limiting.

For future research, I would recommend developing different metrics for measuring either a given unit’s exposure to artillery fire or said unit’s losses. In this post I have only incorporated casualties as a percentage of total soldiers participating in the charge, and it could be worth retooling analysis to focus on finer details like differences in killed, wounded, or captured soldiers. I also do not have any real training in statistics, so people who actually know what they’re doing when it comes to the analysis can improve on what I demonstrated in this article.

Analytic methods similar to the ones I’ve used here could be applied to other artillery-opposed infantry assaults from the war (at Kennesaw Mountain, Fredericksburg, Cold Harbor, or Missionary Ridge for an actually successful assault) or from the broader late-19th century period. The accumulation of more data could lead us to more generalized, evidence-based conclusions on the impact of 19th century field artillery in battle.