Salvage workers are slowly pulling the huge, corroded South Korean ferry above the sea surface on Thursday, about three years after it sank on a routine voyage to a resort island, killing more than 300 people, mostly high school students.

The sinking, the country’s deadliest maritime disaster in decades, caused an outpouring of national grief and a rare bout of soul-searching on long-ignored public safety and regulatory failures.

A look at developments in the April 2014 ferry disaster and its aftermath-

April 16, 2014- The Sewol carrying 476 people, mostly students from a single high school on a field trip to a southern resort island, begins sinking off South Korea’s southwestern coast.

April 18, 2014- The ferry completely sinks below the surface.

April 19, 2014- Prosecutors detain the ferry’s captain and two other crew members for alleged negligence of duty, maritime law violation and other wrongdoing.

May 19, 2014- President Park Geun-hye says she will disband the coast guard for its purported botched rescue works. Critics accuse Park of making the stunning announcement to shift attention from withering criticism of her handling of the sinking.

July 22, 2014- Police say the badly decomposed body of a fugitive billionaire owner of the ferry has been found. Authorities had launched a manhunt for Yoo Byung-eun because they believe his alleged corruption contributed to the sinking.

Nov. 11, 2014- The government ends an underwater search for nine bodies still missing from the disaster.

Aug. 4, 2015- The government agrees to an 85.1 billion won ($73 million) deal with a Chinese-led consortium led by China’s state-run Shanghai Salvage Co. to raise the Sewol.

Nov. 12, 2015- The Supreme Court upholds a life sentence for the captain of the ferry for charges including homicide by ““willful negligence.” Fourteen other crewmembers receive prison terms of 18 months to 12 years.

March 22- Salvage workers start to lift the ship after hours of preparations and tests.

March 23- Parts of the Sewol are raised above the surface for the first time in more than 1,000 days.