KRI Nanggala (402), a Type 209 diesel-electric submarine of the Indonesian Navy, was conducting military drills in the Bali Sea when it reported a loss of contact. The submarine had requested permission to dive, initiating an operation that would involve various search and rescue missions from the Indonesian Navy and other international forces. After several days of searching, debris and the submarine’s remains were eventually discovered at a depth of over 800 meters, confirming the loss of all 53 crew members aboard.

The Nanggala was originally commissioned in 1981 and had recently undergone renovations. Its mission was critical to showcasing Indonesia’s naval capabilities in regional security and solidifying the nation's maritime defense strategy. The sinking raised questions about underwater safety protocols, the condition of aging military vessels, and the readiness of naval forces to carry out such operations. One notable aspect was the extensive international cooperation in the search, with assistance offered by several countries including Singapore and Australia, highlighting the regional implications of maritime security issues.

This incident prompted the Indonesian government to conduct an investigation to determine the causes of the sinking, which included mechanical failures, operational protocols, and crew training practices. The sinking of KRI Nanggala (402) also reignited debates about the adequacy of Indonesia's naval fleet and the necessity for modernization in the face of increasing territorial disputes in Southeast Asia, especially in the South China Sea.