Secluded on the top floor of a bombed-out four-story apartment building north of war-scarred Fallujah, Iraq, Navy SEAL sniper Chris Kyle is just getting comfortable.

It’s November 2004. Thanksgiving time. The second battle of Fallujah has launched, and Kyle is swaddled in silence atop an upturned baby crib, studying the enemy through a Nightforce 4.5-22 power scope attached to a .300 Win Mag rifle.

He’s feeling badass.

“We just got word that the president of Iraq said that anyone left in the city is bad — meaning, clear to shoot,” he recalled for The Post. “From that point on, every fighting-age male was a target.”

That was just fine with Kyle, who spent five weeks in the hideout, protecting Marines on the ground and bagging seven confirmed kills — adding to his official total of 160, making him the deadliest sniper in US history.

“After the first kill, the others come easy. I don’t have to psych myself up, or do anything mentally — I look through the scope, get the target in the cross hairs and kill my enemy before he kills one of my people,” Kyle writes in his new autobiography, “American Sniper.”

During his 10-year career as a member of SEAL Team 3, Kyle, 37, saw action in every major battle during Operation Iraqi Freedom.

He became known among his fellow SEALS as “The Legend.”

The enemy was less complimentary.

In Ramadi, insurgents put an $80,000 bounty on his head and branded him “Al-Shaitan Ramadi” — “The Devil of Ramadi.”

“That made me feel like I was actually doing my job and having an effect on the war,” he said.

In north-central Texas, Kyle grew up dipping tobacco, riding horses and hunting deer, turkey and quail — a cowboy at heart.

He got his first gun at 8 years old — a bolt-action 30-06 rifle.

The son of a Sunday-school teacher and a church deacon, Kyle credits a higher authority for his longest kill.

From 2,100 yards away from a village just outside of Sadr City in 2008, he spied a man aiming a rocket launcher at an Army convoy and squeezed off one shot from his .338 Lapua Magnum rifle.

Dead. From more than a mile away.

“God blew that bullet and hit him,” he said.

For Kyle, the enemy is a “savage” — there’s no room for gray, only black or white.

His Charlie platoon even adopted the insignia of the comic-book vigilante The Punisher, spray-painting skulls on their body armor, vehicles, helmets and guns.

“You see us? We’re the people kicking your ass. Fear us, because we will kill you, motherf–ker,” he writes.

The married father of two is now president of Craft International, an outfit that provides sniper and security training for the US military.

He teaches what’s required to take that perfect shot: Study the terrain, correct for elevation and wind, prepare for the vibration after the shot, and keep in mind the Coriolis effect, the effect of the rotation of the Earth on a bullet’s trajectory.

“You need skill to be a sniper, but you also need opportunity. And luck,” he said.

He retired a chief petty officer, and along the way, collected an armload of hardware, including two Silver Stars and five Bronze Stars with valor.

“That’s just candy,” Kyle said. “That’s not why we were there.”