The central meaning of Liam O'Flaherty's short story "The Sniper" is the vicious unpredictable nature of war and the cruel toll it takes on the soldiers who fight. The Republican sniper is responsible for the deaths of three people in the short time span of the story. He may have killed many more in his role as a sharp shooter on a Dublin rooftop during the Irish Civil War. 

The war in the streets of Dublin is an unpredictable chess match. Even the lighting of a cigarette could lead to death. Soldiers and civilians alike are in danger in the chaos of battle. The sniper kills a woman who is pointing out his position, an armored car commander who foolishly reveals himself and, after staging a diversion, the Free-State sniper. The death toll, however, wears on the sniper. 

After tricking the enemy sniper into showing his position and killing him, the Republican sniper breaks down. He temporarily loses his head and almost kills himself when he throws down his pistol. The stress of battle sends him into a temporary madness. O'Flaherty writes,

Weakened by his wound and the long summer day of fasting and watching on the roof, he revolted from the sight of the shattered mass of his dead enemy. His teeth chattered, he began to gibber to himself, cursing the war, cursing himself, cursing everybody.

O'Flaherty never reveals the sniper's reaction when he discovers the dead man is really his brother. Obviously it would have been something extremely difficult to live with. The cruelty and unpredictability of the war must have been a crushing blow to his spirit.  

Analyze the theme of "The Sniper."

The primary theme of "The Sniper" is a demonstration of how war is a dehumanizing experience. The transformation that the sniper goes through attests to this theme.  While he starts out completely immersed in his task and his responsibility of "taking out the target," his enemy sniper, he comes to realize the futility of such an action.  The theme is best seen when the sniper sees the consequences of his action when he examines the body of the enemy sniper that he has shot down.  Where there used to be a feeling of accomplishment and pride, zeal in its certainty, there is a revelation of emptiness and this hollowness is intrinsic to war, in general:  

The sniper looked at his enemy falling and he shuddered. The lust of battle died in him. He became bitten by remorse.  The sweat stood out in beads on his forehead. Weakened by his wound and the long summer day of fasting and   watching on the roof, he revolted from the sight of the shattered mass of his dead enemy. His teeth chattered, he began  to gibber to himself, cursing the war, cursing himself, cursing everybody.

It is here in which the theme of the story reveals itself. War is a dehumanizing experience.  It is one that severs connections between human beings.  It turns- literally, by the story's end- brother against brother.  The sniper's realization of this is of vital importance and represents the fundamental theme in the story.  Through the characterization of the sniper and his change, this theme can be analyzed in both subjective and historical contexts.

What is the theme of "The Sniper"?

Two obvious themes are that of (1) brother pitted against brother in war and (2) the objectification and dehumanization of faceless, identity-less participants (warriors, but also victims) in war. A third more subtle yet more dramatically central theme is that the heat of war blinds participants to the reality of murdering living individuals.

To explain the first theme, the theme of brother against brother is a literal theme and a metaphorical one. In civil wars, literal brothers may choose opposite sides and face each other across firing lines. In all wars, metaphorical brothers, who are common members of the human race, face each other across firing lines.

To explain the second theme, the theme of objectification and dehumanization is metaphorical; the enemy is seen to be like nothing. The enemy is seen to have no object in their existence, no humanity in their individuality as they are hunted and shot down, whether enemy or informant, whether old or young, whether male or female, whether student or worker. This objectification and dehumanization hits both warrior and victim. The warrior abandons an innate sense of humanity in order to live "enveloped in darkness" with the "cold gleam of the fanatic" as [in this story] a sniper. The victim is seen as the "enemy" and nothing more.

To explain this third subtle and more central theme, the theme of blindness to the reality of doing murder in war is representational of the dependence of acts of war upon first obliterating all trace of fear--even fear of losing one's own life--upon obliterating the fear of living with and "looking at death." 

They were deep and thoughtful, the eyes of a man who is used to looking at death.

This fearlessness, even of one's own death, is needed for the act of cold-blooded killing in war, for cold bloodedly aiming in the dark--a trained, skilled, sure-shot sniper--at an old woman, at a man, at one's own brother. The sniper represents this great fearlessness. Snipers must be, above all other modern warriors, cool, steady of nerve, impersonal, with eyes that are "used to looking at death."

This theme is dramatized when in the story the sniper has a moment of thunderous fear. Weakened by fasting and having been wounded, he recoils, "revolts" from the horror of watching his enemy die, falling, tumbling "over and over in space," from the rooftop opposite.

Weakened by his wound and the long summer day of fasting and watching on the roof, he revolted from the sight of the shattered mass of his dead enemy.

His recoiling, revolting horror and his fear--of what he has done as much as of what might be done to him--compel him to "hurl" his revolver down at his feet. It goes off, sending a bullet past him.

The shock of the gun's report and the whizzing bullet snaps him out of deep fear, dispelling from him the "cloud of fear" that exploded in his mind at the sight of his tumbling, dead enemy. His nerves steady and he can resume being "the sniper"; he can escape the fear of being a man.

The subtle though overarching theme, then, in this story is that the heat of war blinds warriors to the reality of doing murder. When the blinders are removed, as by watching a skilled man, though an enemy, tumble in his death agony, or as by looking in a dead enemy's face and finding a brother, fear is unleashed in a mushroom cloud of horror that recoils, revolts against and rejects the machines of war.

The lust of battle died in him. He became bitten by remorse. The sweat stood out in beads on his forehead. ... [He] revolted from the sight of the shattered mass of his dead enemy. ... Then the sniper turned over the dead body and looked into his brother's face.

What is the underlying theme of The Sniper?

The key underlying theme O'Flaherty exposes in "The Sniper" is the absolute futility, and unnaturalness, of civil wars such as the one being fought in Ireland at the time the story is set. Wars of this sort create such division in families that the two brothers in the story are fighting on opposite sides; the protagonist inadvertently kills his brother, without ever knowing it was him, because their identities as Republicans and Unionists have depersonalized them so entirely. He does not kill his brother by accident—on the contrary, he kills him deliberately, because of what he is in political terms. He may not know that this is his brother in literal terms, but he certainly knows that he is, in the broader sense, his brother, a fellow Irishman. The outcome of the story, a brother killing his own flesh and blood, is a metaphor for the broader war as a whole. This type of civil conflict drives rifts between families, but moreover drives an unnatural rift between Irishmen based upon their political alliances.