In "The Artilleryman's Vision," why might Whitman have been interested in this particular soldier?

By the outbreak of the Civil War, Walt Whitman had already published the first few editions of the poetry collection that became his life's work, Leaves of Grass. During the course of the war, he traveled to Washington DC to take care of his wounded brother, who was a Union soldier. Whitman stayed in the area for years, nursing and comforting soldiers in hospitals. By Whitman's own estimation, he made approximately 600 hospital visits, meeting somewhere between 80,000 and 100,000 wounded soldiers. As a result, he got a profound firsthand look at the suffering and trauma that the soldiers went through.
In 1865, he published a collection of poetry called Drum-Taps, of which "The Artilleryman's Vision" was a part. In this collection, Whitman presents scenes, sometimes horrific, from the Civil War. Drum-Taps later became a section in the ever-expanding Leaves of Grass.
The Merriam-Webster Dictionary simply defines artilleryman as: "A soldier in the artillery." In the Civil War, heavy artillery units consisted of placements of artillery at garrisons and seacoasts. Field artillery units were more mobile and consisted of weapons such as cannons that could be moved from place to place. In the poem, it sounds as if the artilleryman would have been part of a field artillery unit.
Artillerymen were common in the Civil War, and they would have often found themselves in the midst of noisy, bloody battles. Whitman uses the image of an artilleryman for this reason. He is able to describe the terrors that a traumatized veteran might experience, even when he lies awake surrounded by his family, if he begins to relive the sights and sounds of the battlefield.
It's possible that Whitman had one particular soldier (of the numerous soldiers that he visited) in mind when he wrote the poem, but there is no way now to know this for sure.
https://poets.org/poet/walt-whitman

https://www.biography.com/writer/walt-whitman

https://www.cwartillery.com/FA/FA.html