On March 20, 2003, Kyle’s team flies into Iraq in a helicopter, prepared with their diver propulsion vehicles and protective gear. Despite intelligence claiming otherwise, they encounter heavy anti-aircraft fire. Their mission is to secure the al-Faw oil refinery as part of the opening assault of the US-led invasion of Iraq, codenamed “Operation Iraqi Freedom.” Landing, their vehicles get stuck in oil-soaked mud—another intelligence failure—so the SEALs dismount and proceed on foot, setting up defensive positions. Realizing they have landed inside the Iraqi defensive perimeter with enemy forces surrounding them, Kyle returns fire with his M-60. Heavily outnumbered, the team calls in air support from A-10 Warthogs and other aircraft, which devastates the Iraqi forces. After the fight, the unit rests.

The next day, while Kyle and his colleague go out to check the base perimeter, an Iraqi mortar round lands nearby but fails to detonate. When white smoke pours from the impact, a gas alarm is raised and British guards of the coalition forces close the gate against the SEALs as quarantine against contamination. The gate is opened when the smoke is cleared as a false alarm.

Kyle’s team moves north to the Shatt al-Arab river to watch for enemy boats. From an abandoned Iraqi border station, an Iranian soldier fires a single shot at them each night but their requests to return fire are repeatedly denied. After a frustrating week of inactivity, they return to Kuwait with low morale, fearing they will be replaced by SEAL Team 5 before seeing more action. Instead, they are assigned to support Marines near Nasiriya.

Kyle states that the US Navy Marines are always aggressive fighters, while he considers the Army units to be more variable. His team reconnoiters, engaging in a brief firefight. After taking fire again that night, the risk-averse Marines commanding officer (CO) orders them back, to Kyle’s disgust. He reflects on a later episode when, after a grueling firefight, Marines raised an American flag while the National Anthem played, reinforcing their shared patriotism.

Kyle describes his intense hatred of the Iraqi fighters. He criticizes the Iraqi insurgents’ “fanaticism” and describes finding a mass grave containing “murdered” US soldiers and Marines. Briefly terrified he will find his brother among the dead, he later learns his brother was deployed elsewhere in Iraq. At other sites, Kyle’s team discovers chemical weapon precursors (chemical ingredients) and fighter jets buried in the desert by the deposed ex-President of Iraq, Saddam Hussein.

During a firefight at a building compound, Kyle’s 16-man platoon is surrounded by several hundred Iraqis. Fighting through the night, they believe they will be killed in minutes; as Kyle prepares for death, Marines arrive, and the battle is won. This proves to be their final major action, as their CO pulls them back. Kyle spends his last two weeks feeling like a “coward” and considers leaving the Navy.

The narrative switches to Taya’s voice. After Kyle returns home, she describes his anger at American indifference to the war and his violent sleep patterns. Kyle stays home for a week, experiencing several post-traumatic episodes such as diving under his desk imagining a Scud alert, or mistakenly tracking himself as an intruder through his own house.

Kyle decides not to quit the Navy despite his frustrations with the leadership. He attends SEAL sniper school and describes mental and physical pressures of the program. The curriculum begins with computers, cameras, and observation skills before moving to stalking, the hardest portion, where most students fail. Kyle nearly fails due to a lack of patience but passes after realizing he needs to chew tobacco during tests, establishing a superstitious ritual.

Kyle details the weapons he is trained on: the Mk-12 (5.56mm), Mk-11 (7.62mm), .300 Win Mag (his primary), and .50 caliber (which he dislikes). He explains that SEAL snipers observe and gather intelligence as well as shoot. He learns to adjust for elevation and uses Nightforce scopes with various magnification options. Kyle graduates in the middle of his class, which he says shows that opportunity and luck matter as much as skill in accumulating kills.

During training exercises, Kyle has close encounters with dolphins trained for harbor defense, a sea lion guarding piers, and sharks. In one incident, a shark attacks his fin while he is planting a mine. In another, sharks surround his Zodiac after killing a sea lion. His team gets lost at sea for a night due to wrong coordinates but is rescued. Kyle gets his first tattoo—a frog skeleton on his back—to honor fallen SEALs.

Kyle and Taya decide to start a family. Her pregnancy goes smoothly, but labor is complicated by a low platelet count that prevents pain medication. After 16 hours of natural childbirth and concerns about complications, their son is born healthy.

Soon after, Kyle attends navigation school reluctantly, knowing navigators often miss direct action. However, his navigation skills will get him to Iraq ahead of his platoon.