Operations to lift the sunken ferry Sewol from the seabed began this week, nearly three years after it capsized off the country's southwestern coast and killed more than 300 people aboard.

   The following is a summary of the key events surrounding the disaster and the consequences it has had for South Korean society as a whole.

-- How the ferry sank

The Sewol, a 6,825-ton passenger ferry, left Incheon, west of Seoul, for the southern island of Jeju on April 15, 2014. It was carrying 476 people, including 324 students of Danwon High School in Ansan, south of Seoul. The students and their teachers were on a field trip to the resort island.

   The ship left port 2.5 hours behind schedule due to fog.

   At 8:48 a.m. April 16, the ferry made a sharp turn after sailing through the Maenggol Channel, which is notorious for its strong underwater currents.

   At 8:52 a.m., a student on the ship called 119, the emergency hotline, sending a distress signal that the boat was sinking. His first words were "Save us, please!" He later said, "The ship is tilting."

   It took six more minutes for the nearby Coast Guard in Mokpo to register the call. At 9:06 a.m., the Jindo Vessel Traffic Service made contact with the ferry and began to take control of the situation.

   Rescue operations kicked off with the involvement of the Coast Guard, the Navy and dozens of fishermen and fishing boats in the vicinity.

   The first report on the sinking was broadcast on news channel YTN at 9:19 a.m.

   At 9:39, the ferry's chief engineer and six other engineers escaped on the first rescue boat sent by the Coast Guard. Several minutes later, the ferry's captain also abandoned ship and was rescued by the Coast Guard.

   By 9:50, 80 people were rescued. Four minutes later, the port side was completely immersed in the water as the ship tilted more than 64 degrees.

   At 10:00, then President Park Geun-hye gave her first order through her spokesman to do everything possible to save the people on the ferry. The government set up a task force to directly handle the situation.

   At 10:21, some 40 people were rescued from the sinking ferry.

They were the last to be rescued before the Sewol capsized at 10:31.

   Late in the afternoon, around 5:30 p.m., President Park visited the government task force to be briefed on the rescue operations and issue another order to do everything possible.

   The ferry's operator, the government and the Coast Guard gave conflicting reports on the exact number of people on the boat and the number of people who had been rescued.

   Search operations resumed past midnight using flares, but the number of casualties climbed. By 9:00 a.m. April 17, eight people were confirmed dead, while 288 others remained unaccounted for.

   On April 18, the Sewol was fully immersed under water and sank completely at around 11:50 a.m.

   Only 172 people were rescued. Of the others, 295 were confirmed dead and nine others have remained missing since.

 -- Why the disaster shook the nation

 The nation's worst maritime disaster laid bare a number of deep-rooted problems in South Korean society and politics. The government took most of the blame for bungling its initial response to the sinking with delayed rescue operations, botched coordination, and conflicting reports on passenger and casualty numbers.

   It revealed how Koreans are used to ignoring regulations for the sake of expediency and sometimes profit.

   The tragedy also exposed the sordid ties between regulators and businesses in a country where government officials often take jobs related to their former duties after retirement.

   Such ties among the "bureaucratic mafia" were blamed for lax safety checks on the Sewol, which was found to have been carrying too much cargo and had been remodeled beyond its safety limits.

   The nation's safety management system was found to be poorly in place and barely functioning. Few people were prepared to respond effectively to a disaster on the scale of the Sewol.

   There was nationwide soul searching over the apparent lack of ethics not only in those in high positions of society but also among the general public. The ferry's captain who abandoned ship was a case in point.

   The number of casualties was large, and the fact that the majority of them were young students caused greater mourning.

 -- How the nation responded

Then Prime Minister Chung Hong-won offered to resign to take responsibility for the poor handling of the disaster. He was retained by Park.

   On May 19, Park announced the dissolution of the Coast Guard.

   The prosecution arrested the captain Lee Jun-seok and 14 other crew members. Lee was sentenced to life in prison for murder and the Supreme Court confirmed the sentence in November 2015. The other crew members also received prison terms.

   Prosecutors also launched an investigation into the ferry's owner Yoo Byung-eun and his family over their alleged corruption and other illegalities, which were believed to have contributed to the disaster.

   Amid a nationwide manhunt, Yoo was found dead in a plum field in July.

   In November, the National Assembly passed a special bill aimed at uncovering the truth behind the sinking. The government was reorganized with the launch of the Ministry of Public Safety and Security, which was tasked with overseeing disaster management.

   Criticism of Park persisted amid rumors she underwent plastic surgery or other cosmetic treatments during the early hours of the sinking. The rumors were caused by her apparent absence from duty during the seven hours from when the sinking was first reported until she appeared at the government task force around 5:30 p.m.

   In December 2016, the National Assembly passed an impeachment motion against Park over a corruption scandal involving her and her close friend Choi Soon-sil. The resolution cited her failure to protect lives and faithfully execute duties during the ferry sinking as one of the reasons for her ouster.

   In March 2017, the Constitutional Court upheld the impeachment and removed Park from office. On the Sewol, however, the court said it is not in its jurisdiction to determine whether she faithfully carried out her duties. It also said it is difficult to recognize that the president has a specific responsibility to take part in rescue operations in a disaster threatening people's lives. (Yonhap)