North Korea's new young leader navigated a tank and watched as jets tore through the skies in footage aired Sunday on state television, in the latest effort to show that he has the support of the powerful military.

Kim Jong Un, who was named "supreme leader" of North Korea's people, ruling Workers' Party and military following the death last month of his father, Kim Jong Il, was shown maneuvering a tank, observing firing exercises and posing for photographs with soldiers in footage that was shot before his father's death and aired as a documentary Sunday.

The documentary, which aired on what is believed to be Kim Jong Un's birthday, is the second in a week to show Kim with military units, and underlines his pledge to carry out his father's "military first" policy. A week ago, footage showed Kim paying a New Year's Day visit to a premier tank division with strong historical and family ties.

Late leader Kim Jong Il elevated the prominence of the Korean People's Army after taking power following the 1994 death of his father, North Korea founder Kim Il Sung. North Korea, which has a population of 24 million, now has one of the world's largest armies, with 1.2 million military personnel.

The footage shown Sunday showed father and son, both in heavy winter parkas, speaking with military officers. State TV did not say when the video was taken.

Since Kim Jong Il's death of a heart attack Dec. 17, the process to install his son as leader has been quick, with top military and party officials wasting no time in pledging their loyalty to young Kim Jong Un.

Kim Jong Un, a graduate of Kim Il Sung Military University, was confirmed as his father's choice among three sons to succeed him when he was made a four-star general in September 2010. He was also made a vice chairman of the Central Military Commission of the Workers' Party of Korea.

Kim Jong Un is believed to have turned 28 or 29 on Sunday, though his exact birth date has not been confirmed by the North Korean government.