On March 8, 2025, North Korea disclosed, for the first time, the images of its strategic nuclear submarine under construction. This development shows the rapid advancement of the North’s nuclear submarine program - initiated as an official strategic priority four years ago. Amid the escalating security threats posed by the rapid advancement of North Korea’s nuclear capabilities, South Korea needs to urgently formulate and implement countermeasures. North Korea, in its pursuit of advanced nuclear capabilities, is progressing toward an underwater-based second-strike capability by developing new submarine technologies and investing in underwater weapon systems. The successful completion of a strategic nuclear submarine has presented substantial technical obstacles. However, emerging reports suggest that Pyongyang may be circumventing these difficulties through strategic cooperation with Russia. That is, the potential transfer of small modular reactor (SMR) technology from Russia to North Korea deserves close monitoring. To achieve the denuclearization of North Korea reaffirmed by the second Trump administration, the Korean government needs to scale up diplomatic efforts with heightened vigilance. In conjunction, it should accelerate trilateral defense coordination with the U.S. and Japan by operationalizing the Nuclear Consultative Group (NCG) and swiftly deploying SM-3 interceptors on Aegis-equipped Destroyers. 

1. Introduction

2. An Analysis of the Advancement Track of North Korea’s Nuclear Capabilities

3. Pillar Ⅰ of North Korea’s Second-Strike Capability: Progress in SLBM Development

4. Pillar Ⅱ of North Korea’s Second-Strike Capability: Submarines in Stock

5. Outlook and Tasks Ahead: How to Advance Nuclear Security?