North Korea's sideways-launch warship accident

What happened to the new North Korean warship during launch, and why did it sink?

The stern appears to have snagged during a sideways launch while the bow kept moving, causing the ship to roll and sustain damage.

Sideways launching is an efficient way to launch a ship where space is confined, but a snag can leave one part of the hull moving while another stops. The suggested failure sequence is that the stern stopped or lacked momentum while the bow continued, causing the ship to roll. Whether the engines and complete power plant had already been installed was still disputed, and their absence could affect the hull's balance. A separate disagreement concerns classification: one participant suggests a coastal-defence destroyer, while Clarke rejects that category and prefers an air-warfare frigate or littoral combatant.