Chile leverages US exercise to enhance regional deterrence and submarine warfare skills.

According to information published by the Chilean Navy on August 31, 2025, the submarine SS-20 Thomson has arrived at the U.S. Naval Base in San Diego following an extended voyage from its homeport in Talcahuano. The deployment marks Chile’s official participation in the 2025 edition of the Diesel Electric Submarine Initiative (DESI), a long-standing multinational naval training exercise focused on anti-submarine warfare and operational interoperability with the U.S. Navy. Over the next five months, the Thomson will operate alongside units from the U.S. Navy’s Third Fleet in one of the most complex and strategically significant maritime training environments in the Pacific.
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 The SS-20 Thomson is a diesel-electric attack submarine that forms a critical part of Chile’s undersea deterrence capability (Picture source: Armada de Chile)

Commissioned in 1984, the SS-20 Thomson is a diesel-electric attack submarine that forms a critical part of Chile’s undersea deterrence capability. It has a surfaced displacement of 1,260 tons and 1,390 tons when submerged, and measures 59.5 meters in length with a draft of 5.5 meters. Propelled by a conventional powerplant generating 2,400 horsepower on the surface and 4,600 horsepower submerged, the submarine reaches speeds of up to 11 knots on the surface and 21.5 knots when submerged. Armed with eight 21-inch torpedo tubes, the Thomson is configured for a range of combat missions, including anti-submarine and anti-surface warfare, intelligence gathering, and special forces deployment. Its low acoustic signature enhances its survivability in contested waters, while its sonar suite enables effective detection and engagement of hostile contacts.

The departure of the Thomson was marked by a formal send-off ceremony attended by senior naval leadership, including Vice Admiral Raúl Zamorano, Chief of the Navy General Staff, and top commanders from Chile’s Submarine Force. The ceremony highlighted the mission's strategic intent to enhance joint capabilities and the professionalism of the 45-person crew led by Commander Gonzalo Álvarez. Prior to departure, the submarine’s personnel completed an intensive period of technical and logistical preparations, underscoring the operational demands and expectations of this high-level bilateral engagement.

The DESI program was initiated by the U.S. Navy to address the growing need for realistic anti-submarine warfare (ASW) training, particularly against diesel-electric submarines which offer unique challenges due to their low acoustic signatures. For the Chilean Navy, participation in DESI offers an opportunity to sharpen its tactical performance in scenarios involving coordinated engagements against surface ships, nuclear submarines, and maritime patrol aircraft specialized in ASW missions. Additional training elements include sea control operations, coordinated fleet maneuvers, and NATO-standard submarine rescue exercises, which collectively reinforce Chile’s capacity to operate alongside major naval powers.

Chile’s participation in DESI dates back to 2006, making the 2025 iteration part of a nearly 20-year history of sustained cooperation with the United States in the undersea domain. This continuity has allowed the Chilean Submarine Force to maintain a high state of readiness, while also supporting broader regional security objectives by projecting presence in the Pacific and strengthening multilateral naval frameworks. The Thomson’s deployment underscores the Chilean Navy’s strategic emphasis on maritime partnerships and its commitment to operational excellence within allied defense architectures.

The arrival of the Thomson in San Diego for DESI 2025 confirms Chile’s ongoing role as a credible regional partner in maritime security and underlines the value of diesel-electric submarines in shaping modern ASW strategies. Through this engagement, the Chilean Navy not only reinforces its interoperability with a peer naval power but also contributes meaningfully to deterrence and stability in a dynamic strategic environment.