London:  With 255 kills, 160 of them officially confirmed by the Pentagon, Chris Kyle, the retired Navy Seal sniper, is the deadliest marksman in US military history.

Kyle hesitated the first time he killed a person at long range with a rifle. It was a woman who was about to attack a group of US Marines with a hand grenade.

The US Navy SEAL was overlooking an Iraqi town from a shabby building as US forces were still invading the country, before Saddam Hussain had been ousted. The Marines didn't see the woman coming.

"Take a shot," Kyle's chief told him. Kyle stammered: "But..." "Shoot!" the chief told him again.

Kyle finally pulled the trigger, the woman dropped the grenade. He shot her again as it exploded.

But after four deployments to Iraq, he learned to stop hesitating and start shooting straight.

The report said that during the Second Battle of Fallujah alone, when US Marines fought running battles in the streets with several thousand insurgents, he killed 40 people.

His feat blows away the previous American record of 109, set by Army Staff Sgt Adelbert F Waldron during the Vietnam war.

Carlos Hathcock, the famed Marine sniper who was the subject of the book 'One Shot, One Kill,' killed 93 people as a long-range sniper in Vietnam.

However, despite the mind boggling number of kills, Kyle is still far from being the deadliest marksman in the world.

That distinction goes to Simo Hayha, a Finnish soldier who killed 542 Soviet soldiers during World War II.

For Kyle's deadly track record as a marksman during his deployment to Ramadi, the insurgents named him 'Al-Shaitan Ramad' -- the Devil of Rahmadi -- and put a USD 20,000 bounty on his head.

The daily said his most legendary shot came outside Sadr City in 2008 when he spotted an insurgent with a rocket launcher near an Army convoy -- 2,100 yards away.

At that distance, 1.2 miles, he fired a shot from his .338 Lapua Magnum rifle. It struck home, knocking the man over dead.

Kyle, who retired from the Navy after 10 years of service, is telling his remarkable story as a deadly marksman in his new book, 'American Sniper,' which hit shelves on Tuesday.

He left the service in 2009, deciding not to enlist in order to "save his marriage", he told his publisher.