Submarines are one of the most important assets in any navy, providing not only strategic advantage, but also create a deterrence effect for potential aggressors. In Indonesia, the submarine squadron and its capability, is designated as a main asset of the Defense Weapon System of Indonesia (ALUTSISTA). In 2021, the Indonesian Navy (TNI-AL) conducted a series of operational testing in the Bali Sea, with submarine KRI Nanggala-402 tasked to conduct a torpedo live firing exercise. However, disaster struck during the preparation phase, and communications were lost with the submarine. An emergency protocol was triggered, with surface vessels and resources were activated to respond to the Search and Rescue (SAR) effort. Due to the time sensitive nature of this event, a diplomatic request was made to friendly countries in the region – countries that Indonesia had close bi-lateral ties – to provide assistance in finding the 56 submarine’s crew. The years of strengthening collaboration with Indonesia’s neighbors, and its defense diplomacy in the region has paid off. Search and rescue teams from across countries within Asia Pacific region joined hands, in sending surface vessels, rescue ships, and planes in support of this effort. KRI Nanggala-402 was finally found at the bottom of Northern Bali Sea, with hull damages and its entire crew has been lost in this unfortunate incident. While the incident highlighted the risks of submarine forces, it also highlights the growing importance of defense diplomacy in the region. The globalized atmosphere in which we live in, means coalition building, and greater international collaboration are essential to creating a safer region. This research uses applies qualitative analysis, in conjunction with a descriptive analytical approach, to draw lessons from crisis, and study defense diplomacy and its intricacies from an Indonesian’s standpoint.