Singapore Expands Submarine Fleet: Adds Two More Invincible-Class Boats to Cement Undersea Dominance

(DEFENCE SECURITY ASIA) — In a major step to solidify its status as the region’s preeminent undersea power, the Republic of Singapore Navy (RSN) will acquire two additional Invincible-class (Type 218SG) submarines, bringing its total to six by the year 2034.

The upcoming boats—custom-built once again by German shipbuilder ThyssenKrupp Marine Systems (TKMS)—signal sustained strategic investment in long-range maritime defence and undersea deterrence by Singapore.

Announced by Defence Minister Dr Ng Eng Hen in March, the procurement underscores Singapore’s long-term vision of developing a technologically superior and future-ready naval force capable of operating in increasingly contested waters.

“These Invincible-class submarines, customised by the Defence Science and Technology Agency (DSTA) to meet Singapore’s operational requirements, are built for shallow and congested tropical waters and are optimised for operation by a lean, highly trained RSN submarine crew,” the Ministry of Defence (MINDEF) said in a statement.

Designed with regional maritime chokepoints in mind, the new submarines will significantly boost Singapore’s ability to protect the Malacca and Singapore Straits—vital arteries for the nation’s trade-dependent economy.

Singapore had previously contracted TKMS in 2013 and 2017 for four Type 218SG submarines, named RSS Invincible, Impeccable, Illustrious, and Inimitable, which form the backbone of its modern submarine force.

To date, two boats—Invincible and Impeccable—have been delivered and are operational in Singapore, while the remaining pair are undergoing trials in Germany and are expected to join the fleet by 2028.

The Invincible-class submarines represent a generational leap from the RSN’s legacy Challenger-class boats and are designed from the keel up to meet Singapore’s demanding requirements for shallow-water operations in tropical conditions.

At the heart of the Type 218SG’s superiority is its X-shaped rudder configuration, a design feature that grants exceptional manoeuvrability in confined littoral environments—an edge critical in Southeast Asia’s dense maritime geography.

With a submerged displacement of approximately 2,200 tonnes and outfitted with advanced Air Independent Propulsion (AIP) using fuel-cell technology, the submarines boast a significantly extended underwater endurance compared to earlier RSN boats.

Each unit is armed with eight 533mm torpedo tubes, capable of deploying heavyweight torpedoes and anti-ship missiles, enabling the RSN to pose a credible threat to both surface and sub-surface adversaries.

Analysts widely regard the Type 218SG as the most modern and capable diesel-electric submarine in Southeast Asia, surpassing regional contemporaries from Indonesia, Vietnam, and Thailand in both size and technological sophistication.

Naval experts also note the close design parallels between Singapore’s Invincible-class and Israel’s Dolphin-II class submarines, both of which are built by TKMS, hinting at shared high-end sensor and combat suite integration.

Dr Ng has publicly acknowledged that operating just four submarines placed a strain on force availability due to intensive maintenance cycles, which are mandatory for platforms operating in such high-stress underwater environments.

“Our submarines undergo strict and frequent maintenance cycles, with thorough inspections. As you can imagine, they operate under extreme pressure—literally. As a result, their operational time is reduced,” he said, noting that other regional navies, including Australia, Indonesia, and Vietnam, operate larger submarine fleets.

The RSN’s decision to expand the fleet comes after successful operational validation of the Type 218SG in tropical conditions, reinforcing confidence in the platform’s performance, reliability, and suitability for Singapore’s unique maritime domain.

The announcement follows the decommissioning of the RSN’s final two Challenger-class submarines—RSS Conqueror and Chieftain—in a formal ceremony at Changi Naval Base in November last year, ending a chapter that began in the 1990s.

Originally built in Sweden as Sjöormen-class submarines by Kockums, the Challenger-class vessels were acquired as Singapore’s first submarine platforms and laid the foundation for its undersea warfare capability.

With RSS Challenger and Centurion already retired in 2015, the transition to an all-Invincible-class force marks a significant generational upgrade and positions Singapore for undersea dominance well into the 2040s.

Currently, RSS Invincible and Impeccable are berthed at Changi Naval Base, with Impeccable arriving in July 2023 and Invincible shortly after in August.

The remaining two boats in the original quartet—Illustrious and Inimitable—are under construction in Kiel, Germany, and are expected to be delivered and commissioned by 2028.

With two more Invincible-class submarines now on order, Singapore will operate the region’s largest and most technologically advanced conventionally powered submarine fleet, further tilting the balance of undersea power in its favour.

This fleet expansion comes at a time when Southeast Asia is witnessing a quiet but intense submarine race, with countries such as Indonesia, Vietnam, Thailand, and the Philippines all seeking to modernise their undersea warfare capabilities amid rising tensions in the South China Sea.

By doubling down on its investment in next-generation undersea platforms, Singapore is not only safeguarding its maritime trade corridors but also sending a clear message of deterrence and technological superiority to both state and non-state actors in the Indo-Pacific.

— DEFENCE SECURITY ASIA