The state audit agency has interrogated the chief of the Navy over a faulty Navy salvage ship that failed to participate in the national rescue operation for the ferry Sewol that sank off the southwest coast in April, a source said Tuesday.

The interrogation of Navy Chief Adm. Hwang Ki-chul is part of the Board of Audit and Inspection's probe into the military's project to construct the first South Korean-built salvage ship Tongyeong, according to the source.

The military completed the construction of the salvage ship with local shipbuilder Daweoo Shipbuilding & Marine Engineering in 2012, but the military has refused to take over the vessel, citing its insufficient sonar system as well as a remotely operated vehicle for underwater maneuvers.

The ship was not sent to the all-out rescue efforts following the ferry tragedy on April 16, which killed more than 300 passengers.

The audit agency has recently launched its investigation into the salvage ship project in order to find out why the 3,500-ton rescue vessel could not be used when it was most needed.

The interrogation of Adm. Hwang, which took place on Sept. 5, was focused on how Tongyeong's sonar equipment was selected, the source said.

"Adm. Hwang was in charge of choosing sonars when he was the chief of the Defense Acquisition Program Administration's vessel project division in 2009. He has been investigated for about four hours in relation to the issue," he said.

The source said the agency has now finalized its on-site investigation and plans to announce its investigation result in November.

A defense ministry official, meanwhile, said that the military may take more than one year to deploy the rescue vessel in actual missions.

"Despite the replacement of the defective equipment, more problems are being found," the government official added. "It is forecast to take more than one year to replace the equipment." (Yonhap)