Korea Sends KSS-III Submarine Ahn Mu to Guam for U.S. Exercise as Regional Tensions Rise.

South Korea is sending the KSS-III submarine Ahn Mu to Guam for Silent Shark 2025, a joint anti-submarine warfare exercise with the U.S. Navy. The deployment highlights the growing ability of Seoul’s indigenous undersea fleet to operate far from home and plug directly into U.S. Indo-Pacific operations.

The South Korean Navy announced on 17 November 2025 that the 3,000-ton KSS-III submarine ROKS Ahn Mu will deploy to waters near Guam for the Silent Shark 2025 combined anti-submarine warfare exercise with the United States Navy. The month-long drill, starting Tuesday, will pair Ahn Mu and two Korean P-3 maritime patrol aircraft with at least one U.S. nuclear-powered attack submarine and P-8A Poseidon aircraft. Silent Shark is hosted by Submarine Force, U.S. Pacific Fleet and has run biennially since 2007 to sharpen joint submarine and maritime air interoperability near Guam, the forward hub for U.S. undersea power in the second island chain.
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The ROK Navy’s KSS-III Ahn Mu combines air-independent propulsion, long-range patrol capability, heavyweight torpedoes and a Korean vertical launch system for land-attack missiles, marking South Korea's first fully indigenous blue-water submarine (Picture source: ROK Navy).

Silent Shark is framed publicly as a theater-level anti-submarine war game. U.S. and Korean navies rehearse complex sequences of submarine tracking, engagement profiles, free-play undersea combat and coordinated aerial ASW, building on earlier iterations that paired Korean diesel-electric boats with U.S. Los Angeles-class submarines around Guam. The 2025 edition unfolds as Washington and Seoul shift toward integrated deterrence, deliberately linking undersea, air and cyber activities; in parallel with Silent Shark, Korea’s Cyber Operations Command and U.S. Cyber Command are conducting a Korea–U.S. Cyber Alliance drill at the NSA’s Friendship Annex in Maryland to stress-test joint responses to simulated cyberattacks against military networks.

At the center of this year’s exercise is Ahn Mu, the second Dosan Ahn Changho-class KSS-III Batch I submarine and the first Korean-designed and built boat to deploy to an overseas combined drill. Displacing roughly 3,750 tons submerged and measuring 83.5 meters in length, the class combines six 533 mm torpedo tubes for Tiger Shark heavyweight torpedoes and anti-ship missiles with a six-cell Korean Vertical Launching System capable of firing Hyunmoo-4-4 submarine-launched ballistic missiles, giving the ROK Navy a genuine land-attack option from a conventionally powered hull. A fuel-cell-based air-independent propulsion module and large battery capacity allow up to about 20 days of submerged endurance and a cruising range on the order of 10,000 nautical miles, while HY-100 steel, anechoic coating and raft-mounted machinery aim to keep acoustic signatures low enough to challenge modern U.S. sonar. Korean acquisition agencies note that Ahn Mu, the first mass-production KSS-III, passed hundreds of harbor and sea acceptance tests before commissioning in 2023, a maturity level that underpins Seoul’s willingness to send it into distant warm-water operations.

This deployment is a first for the Korean Navy not because Seoul has never sent a submarine to Guam, but because earlier Silent Shark rotations relied on 1,200-ton Jang Bogo-class and 1,800-ton Son Won-il-class boats derived from German Type 209 and 214 designs, optimized for the Yellow and East Seas and built under license. Ahn Mu, by contrast, is the flagship product of a fully indigenous design program with more than three-quarters local content and, crucially, the endurance to operate at scale in tropical waters far from Korean ports. The Navy itself underscored that the transit from Jinhae to Guam proves the seafaring capabilities of Korea’s 3,000-ton class submarines, a carefully chosen message that signals the ROKN’s evolution from a peninsula-bound undersea force to an expeditionary contributor to alliance operations.

Korea is pairing that undersea asset with two P-3 maritime patrol aircraft drawn from its 61st Patrol Air Group, likely a mix of P-3C and P-3CK variants. The P-3 is a four-engine turboprop built around long-endurance anti-submarine warfare, combining surface-search radar, electro-optical sensors, electronic support measures and the distinctive magnetic anomaly detector boom in the tail for final localization. ROKN P-3s have been heavily modernized: Korean Air and General Dynamics supplied VENOM multi-static acoustic processors, while a 2025 upgrade added Ku-band beyond-line-of-sight SATCOM terminals, giving crews high-bandwidth links to Korean and allied command networks over the open ocean. In Silent Shark, these aircraft will seed and monitor extensive sonobuoy patterns, classify contacts and pass precise tracks to both Ahn Mu and the U.S. submarine, effectively acting as the exercise’s airborne quarterbacks in the undersea hunt.

On the U.S. side, Pacific Fleet has not publicly named the specific submarine involved, but the asset will almost certainly come from Submarine Squadron 15 at Naval Base Guam, which currently fields four Los Angeles-class fast-attack submarines and the forward-deployed Virginia-class USS Minnesota. Los Angeles-class boats displace roughly 6,900 tons submerged, exceed 25 knots, and carry Mk 48 heavyweight torpedoes, Tomahawk land-attack missiles and Harpoon anti-ship missiles fired from four 533 mm tubes and, in later flights, a 12-cell vertical launch system. The newer Virginia-class, described by U.S. commanders as the most flexible attack submarine in the fleet, marries a long-life S9G nuclear reactor, pump-jet propulsion and advanced sonar with 12 Tomahawk-capable vertical launch positions and four torpedo tubes, giving it superior stealth and multi-mission reach across the Indo-Pacific. Above them, U.S. P-8A Poseidon aircraft bring jet-powered speed, AN/APY-10 radar, a modern EO/IR turret, high-capacity acoustic processors and an internal bay capable of carrying up to five Mk 54 lightweight torpedoes plus Harpoon missiles on wing pylons.

The P-8A operates with a full suite of radios and tactical data links, including Link 16, Link 11 and wideband SATCOM, designed explicitly to share real-time tracks and targeting data with allied ships and submarines. Korea’s upgraded P-3s, now equipped with modern digital mission systems and beyond-line-of-sight connectivity, can plug into the same architecture, feeding a fused undersea picture to both U.S. and ROK command centers. In practice, that means a Korean P-3 can detect a contact on sonobuoys, push the track over secure data links to a U.S. P-8A or the submerged Minnesota, and then watch as the nuclear-powered boat maneuvers at speed to an attack position while Ahn Mu lurks nearby as an opposing red-force. Each side alternates roles over the month, testing whether a Korean diesel-electric submarine and a U.S. nuclear attack submarine can operate inside a shared kill chain without fratricide or gaps in coverage.

Batch II boats, beginning with the recently launched 3,600-ton Jang Yeong-sil, will add lithium-ion batteries, increased automation and ten vertical launch cells, while a planned Batch III is expected to push displacement and missile capacity even further. Seoul has already floated export-oriented variants to partners such as Canada, signaling that KSS-III is intended as both a national strategic asset and a tool of defense-industrial diplomacy. For Washington, training a sophisticated conventional submarine like Ahn Mu alongside forward-deployed U.S. SSNs from Guam fits squarely within integrated deterrence, reinforcing a network of allies whose undersea forces can operate from the first island chain out to the Philippine Sea and back. If Ahn Mu’s deployment goes smoothly, Silent Shark 2025 will likely be remembered inside the ROK Navy as the moment its indigenous submarine force stepped confidently into blue-water alliance operations. For U.S. planners, it is a live laboratory in which to see whether Korean-built boats, legacy P-3s, cutting-edge P-8As and forward-deployed nuclear submarines can maintain a seamless undersea kill chain across thousands of kilometers of contested ocean.

Written by Evan Lerouvillois, Defense Analyst, Army Recognition Group.

Evan studied International Relations, and quickly specialized in defense and security. He is particularly interested in the influence of the defense sector on global geopolitics, and analyzes how technological innovations in defense, arms export contracts, and military strategies influence the international geopolitical scene.