North Korea's new leader vowed in 2009 to wage war if the country's enemies shot down its long-range rocket, state TV footage showed in the first official word of his role in military operations before his father's death.
The documentary aired on Sunday is the second in a week seeking to highlight Kim Jong Un's experience in leading North Korea's 1.2 million-strong military and was aimed at showing that he was in charge of the armed forces long before his father, former leader Kim Jong Il, died of a heart attack last month.
The son, who is in his late 20s, has moved swiftly into the role of "supreme leader" of the people, the ruling Workers' Party and the military despite questions abroad about how easily he could assume power with only a few years of grooming behind him. Kim Jong Il, in contrast, had 20 years of training when his father, North Korea founder Kim Il Sung, died of a heart attack in 1994.
Where a North Korea under Kim Jong Un is headed is deemed crucial because the country is locked in a long-running stand-off over its nuclear ambitions and is grappling with chronic food shortages. North Korea has tested two atomic devices and is believed to be working towards mounting a bomb on a missile capable of reaching the US
After years of acrimony, Pyongyang and Washington had begun discussions about food aid and how to restart nuclear disarmament talks that were suspended when Kim died last month. The US and North Korea fought on opposite sides of the 1950-53 Korean War and do not have formal diplomatic relations.
The latest footage - shown on a day believed to be Kim Jong Un's birthday - confirmed that he was being groomed as early as 2009 to succeed Kim Jong Il. The choice of Kim Jong Un as successor among the elder Kim's three known sons was not revealed publicly until state media reported in September 2010 that he had been made a four-star general and a vice-chairman of the Central Military Commission of the Workers' Party.
The video showed Kim Jong Un shaking hands with officials at a satellite control centre after scientists launched a rocket in April 2009 that stoked regional tensions and earned North Korea international sanctions and condemnation.
"I had decided to wage a real war if the enemies shot down" the rocket, Kim Jong Un was quoted as saying. A voiceover described Kim Jong Il as saying his son was in charge of the military's anti-rocket interception operations at the time.
North Korea has said it successfully sent a satellite into orbit as part of a peaceful bid to develop its space programme. US and South Korean officials, however, said no satellite or other object reached orbit, and accused the North of using the launch to test its long-range missile technology.
The video also showed Kim Jong Un navigating a tank, observing fighter jets and firing exercises, and posing for photographs with soldiers. He is shown seated in the tank's cockpit and speaking to officers with the hatch cover open.