What information is revealed about the speaker in the opening of Walt Whitman's "The Artilleryman's Vision"?

War, a part of human history since its inception, has left indelible scars on the psyches of millions of soldiers and affected civilians alike. It has been called by various labels over the centuries: “combat fatigue", “shell shock", and presently, “post-traumatic stress disorder” (PTSD). The mental wounds suffered by those exposed to horrific events, especially to the protracted series of violent, physically and emotionally draining events that comprise war, remain a part of the war experience long after the shooting has stopped. The American Civil War was no exception. The seemingly endless sight of young men violently torn apart by musket or rifle rounds, by shrapnel or from bayonets used in hand-to-hand fighting, was not something that could be easily processed. Just as soldiers from World Wars I and II, Vietnam, Korea, Iraq, Afghanistan, and other conflicts have returned home mentally, if not always physically, wounded, such was the case with the predominant conflict of Walt Whitman’s time, the Civil War. His poem, "The Artilleryman’s Vision", depicts the effects of post-traumatic stress disorder on a single veteran of the Civil War. Related in the first-person, Whitman’s narrator is reliving the horrors he witnessed and survived in that traumatic conflict. What we learn about him, then, is presented in the opening stanzas and throughout the text.

As the poem opens, the narrator is lying awake next to his wife, his child, and infant, sleeping close-by. The peacefulness of the night, however, is disturbed in his mind by memories of the war:

WHILE my wife at my side lies slumbering, and the wars are over 
long,

And my head on the pillow rests at home, and the vacant mid-
night passes,

And through the stillness, through the dark, I hear, just hear, the 
breath of my infant,

There in the room as I wake from sleep this vision presses upon me;

The engagement opens there and then in fantasy unreal,

The skirmishers begin, they crawl cautiously ahead, I hear the 
irregular snap! snap!

I hear the sounds of the different missiles, the short t-h-t! t-h-t!
of the rifle-balls,

I see the shells exploding leaving small white clouds, I hear the 
great shells shrieking as they pass . . .

There exists among veterans suffering from PTSD what is known as “the thousand-yard stare", the blankness in the soldier’s eyes as he seemingly stares off into the distance, mentally exhausted from the rigors of combat. It is at night, however, when all is quiet and the room is dark that the visions of the horrors observed become most prominent. And that is what Whitman’s narrator is experiencing. We can surmise from the reference to the infant that he and his wife are young, perhaps newly married following his return from the war. His mind, however, is filled with those images in which bullets pass by his head, men scream in pain, projectiles explode, and smoke from explosions and gunpowder fills the air. That he has grown immune to the suffering around him is suggested in the following passage:

 “The falling, dying, I heed not—the wounded, dripping and red,
   I heed not—some to the rear are hobbling”

What we learn about the narrator of "The Artilleryman’s Vision" is that he is a young combat veteran who has been unable to leave the war behind him. There is a universal sensibility about the images Whitman depicts, and no more needs to be said regarding his narrator’s personal biography. This young veteran of the Civil War has seen too much and he can’t let it go.