CaliToday (21/12/2025): In the deep, cold corridors of the Indo-Pacific, a silent arms race is accelerating. For decades, the United States has held the underwater advantage, but as 2025 unfolds, the math is changing. With the blessing of U.S. President Donald Trump, South Korean President Lee Jae Myung is moving to join the "undersea elite," a move that could fundamentally alter the security architecture of Northeast Asia.
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| Handout image from South Korea's Navy of the Jang Yeongsil submarine that launched on October 22, 2025 in Geoje, South Korea. - South Korea Navy |
The Numbers Game: A Submarine Deficit
The strategic impetus for this partnership is rooted in a sobering reality: the U.S. Navy is increasingly outnumbered in its most critical theater. According to data tracking the global undersea fleet as of July 1, 2025, the naval disparity is stark:
Global Totals: There are approximately 400 foreign submarines currently operating worldwide.
Indo-Pacific Concentration: Roughly 75% (300 vessels) of these submarines are stationed in the Indo-Pacific region.
The Adversarial Block: China, Russia, and North Korea collectively operate 160 submarines.
The U.S. Fleet: By contrast, the U.S. Navy maintains just 49 attack submarines (SSNs) to cover all global responsibilities.
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| US President Donald Trump is presented with the Grand Order of Mugunghwa and the Silla gold crown by South Korean President Lee Jae Myung at the Gyeongju National Museum on October 29. - Andrew Harnik/Getty Images |
With roughly two-thirds of the U.S. fleet available for surge capacity in emergencies, the routine patrol presence is spread thin. Allowing Seoul to operate its own SSNs would effectively outsource the "North Korean watch," freeing American Virginia-class subs to focus on the South China Sea and the Taiwan Strait.
From Lithium to Nuclear: The Technological Leap
South Korea is not starting from zero. In October 2025, Seoul launched the Jang Yeongsil, a 3,600-ton vessel described by the Defense Acquisition Program Administration (DAPA) as the "world’s best diesel submarine."
While the Jang Yeongsil uses advanced lithium-ion batteries extending submergence from the standard 3–4 days to roughly 10–12 days it still pales in comparison to nuclear propulsion. A nuclear-powered sub can stay submerged for years (limited only by food supplies) and travel at significantly higher sustained speeds, allowing it to intercept nuclear-armed Chinese or Russian vessels long before they reach Korean waters.
The "Philadelphia Factor" and the Industrial Tug-of-War
The most contentious detail of the current plan isn't if the subs will be built, but where.
President Trump has signaled that the construction should take place at the Philadelphia Shipyard, which was recently acquired by the South Korean conglomerate Hanwha Ocean. This presents a "win-win" for the U.S. economy, potentially creating thousands of high-paying manufacturing jobs in Pennsylvania.
However, this has sparked a debate in Seoul:
The U.S. Perspective: Building in Philly ensures the U.S. maintains strict control over sensitive nuclear propulsion technology and supports the American industrial base.
The Korean Perspective: Military experts like Professor Kim Dong-yeob argue that building abroad is "essentially no different from buying weapons." Seoul desires a domestic build to secure technology transfer and boost its own industrial ecosystem.
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| Workers construct a grand block of the National Security Multi-Mission Vessel Five (NSMV V), a training platform for state maritime academies, in the grand block shop at the Hanwha Philly Shipyard in Philadelphia, Pennsylvania. - Hannah Beier/Bloomberg/Getty Images |
Geopolitical Ripples: A "Nuclear Domino" Effect?
The regional reaction has been swift. North Korea has already labeled the move a "strategic step toward nuclear weaponization," warning of a "nuclear domino phenomenon" in the region. Meanwhile, China has urged "caution and restraint," fearing that South Korea is positioning itself as the "frontline spear" of a U.S.-led containment strategy.
As South Korea targets a 10-year window to get its first reactor-driven sub in the water, the transition marks a shift from South Korea as a "security consumer" to a "security provider" within the alliance.