'Incident happened at 08.12 local resulting in the death of 55 crew members: 22 officers, 7 officer cadets, 9 petty officers, 17 sailors. Dead include the captain Colonel Xue Yong-Peng.
'Our understanding is death caused by hypoxia due to a system fault on the submarine. The submarine hit a chain and anchor obstacle used by the Chinese Navy to trap US and allied submarines.
'This resulted in systems failures that took six hours to repair and surface the vessel. The onboard oxygen system poisoned the crew after a catastrophic failure.'
https://www.msn.com/en-us/news/world/fifty-five-chinese-sailors-are-feared-dead-after-their-nuclear-submarine-got-caught-in-a-trap-intended-to-ensnare-british-sub-surface-vessels-in-the-yellow-sea/ar-AA1hDPQU