Most people who obtain doctorates do so to advance their career - but that was not the case for one student at Sichuan University.

Huang Zushen, a 74-year-old United States citizen, became a doctoral candidate in the history department at the university's School of History and Culture four years ago.

With the guidance of his tutor, Professor Chen Tingxiang, Huang wrote his dissertation on the development of China's Air Force, from the Chinese Nationalist Air Force in the 1930s to the Chinese People's Liberation Army Air Force in the 1950s.

"He defended his dissertation successfully, with the five-member committee voting unanimously to pass it," said Chen, adding that Huang is the oldest doctoral student in the university's 121-year history.

Li Yujie, a professor of history at Chongqing Normal University and one of the five committee members, said the historical data in Huang's dissertation was unique.

The Chinese Nationalist Air Force came into being in the 1930s. It was almost wiped out during the Japanese invasion during the same period, leading to the Kuomintang rebuilding the Air Force with US assistance.

"Nobody has systematically studied the history. The historical data about US assistance in the rebuilding of the Air Force are in Taiwan and the US. Huang has an advantage in accessing it because of his background and English proficiency," Chen said.

Huang, whose father was a pilot in the Air Force, was born in Chengdu in 1943. He attended a primary school of the Air Force in Dujiangyan, Sichuan, before moving to Taiwan at age 6.

"Many of my relatives were pilots in the Air Force. I lived in residential quarters belonging to the Air Force and attended an Air Force school in Taiwan. I would have been a pilot if it were not for my inability to handle the operating lever of the aircraft," he said.

At 31, Huang, who had emigrated to the US, started a clothing company and became a wealthy businessman.

When he retired from his company seven years ago, he wanted to pursue doctoral studies.

Yin Bo, deputy head of Sichuan University's Institute of Ancient Books, said, "When we had dinner four years ago, he told me his plan, so I introduced him to Chen, a famous scholar of modern Chinese history."

Typically, it takes a student three years to complete a doctoral program, but unlike young students eager to finish their degrees so they can find employment, Huang was able to devote more time to his research.

Chen, who is seven years younger than Huang, said: "In his first year, he lived in an apartment in a building for overseas students at Sichuan University, attending classes for doctoral candidates. In his second and third years, he researched historical data in the US and Taiwan. In his fourth year, he completed his 352-page dissertation, which was more than 200,000 Chinese characters."

When they met for the first time, Chen was afraid a busy study schedule would be too much for a student of Huang's age.

"In order to illustrate he was physically capable, Huang showed off his kung fu skills. He never skipped classes and would sit on the front row in the classroom. He was a role model for other students and the example he set helped boost the attendance rates in class," Chen said.

Huang's children were concerned about his safety as he was well-known on campus for being a multimillionaire. They asked him several times to give up his studies, but he refused.

Huang, who can speak the Sichuan dialect, got along well with his fellow students.

He would refer to students of his grandchildren's age as brother and sister, in the same way young students referred to each other.

"Young students would call him Big Brother Huang," said Chen Fuzhou, a doctoral candidate in the history department.

"He would take walks, visit the secondhand bookstore and dine with young students, and he always wanted to foot the bill when he dined with others," he added.