Cheonan sinking: Paper criticises S Korea military
The South Korean government has issued a report to mark one year since its warship, the Cheonan, was torpedoed with the loss of 46 sailors' lives.
The 308-page White Paper criticises the South's military for failing to raise its alert status to cope with North Korean submarines, Yonhap reports.
Meanwhile, the South has launched a new missile-firing destroyer.
Seoul is demanding the North apologise for the Cheonan incident before cross-border talks can resume.
It also says the North must apologise for shelling Yeongpyeong Island last November.
North Korea denies torpedoing the Cheonan, and says it was provoked into shelling the island by South Korean military exercises in the area.
South Korean media reports suggest the government took the failure to save the Cheonan as a serious blow to its ideas of defence and military strategy.
"On the morning of March 26, the military detected several Yono-class submarines vanished off radar screens after they left a naval base in North Korea's west coast, but no measures were taken to upgrade the alert status on the North's submarines," Yonhap quotes the paper as saying.
At that time, the South's military had "downplayed the activities of North Korean submarines as a routine training mission", the paper said.
South Korea's third destroyer, now embarking on a year of tests before it is combat ready, is equipped with a high-tech Aegis radar and weapons control system.
The 7,600-ton KDX-III destroyer is named the Seoae Ryu Seong-ryong after a leading scholar of the 16th century.
South Korea has built three Aegis destroyers since 2004.