An appeals court on Friday handed down a four-year prison term to a former Navy chief for taking bribes from local firms in return for business favors while in office.

The Seoul High Court convicted retired Adm. Jung Ok-geun for pocketing kickbacks from two former affiliates of STX Group in 2008, but said the amount he received cannot be calculated.

A lower court previously sentenced him to 10 years in jail for receiving 770 million won (US$636,000), which was transferred to the bank account of his eldest son's alleged paper yacht company.

The appeals court, however, said a total of three people held the company's shares, acknowledging it as a legitimate corporate body.

The amount transferred to the account cannot be deemed as what Jung received and the exact economic benefits he earned through the money cannot be calculated, the court said.

He was also acquitted of receiving 60 million won from a defense firm for business favors, citing a lack of credibility in the testimonies provided.

"The nature of the crime is bad in that Jung made companies support his son's firm using his status as Navy chief," the court said.

The court also said there is a need to eradicate unlawful relationships between defense firms and the Navy.

Jung, who served as the Navy Chief of Staff from 2008 to 2010, was indicted in March 2015 on charges of pocketing bribes in return for promising contracts to build the nation's guided missile patrol boat and next-generation frigate.

Jung's eldest son, who actually established the yacht company, also received a two-year jail term, suspended for three years, for his involvement in the crime. (Yonhap)