Invincible-class (Type 218SG)

The Invincible-class, designated Type 218SG, is a class of conventionally-powered diesel-electric attack submarines built for the Republic of Singapore Navy (RSN). The design was jointly developed by the Defence Science and Technology Agency (DSTA), ThyssenKrupp Marine Systems (TKMS), and the RSN. It is derived from the Type 214 export submarine and incorporates design features from the Type 212 submarine and the Type 216 concept. Singapore's Ministry of Defense (MINDEF) selected the design in November 2013 to replace the RSN's Challenger-class and Archer-class vessels. MINDEF contracted TKMS for the first two submarines in November 2013, ordered two more in May 2017, and signed a contract for an additional two in May 2025, bringing the total order to six vessels.

The Type 218SG is configured for littoral operations, securing sea lines of communication, intelligence-gathering, and special operations. To withstand regional environmental conditions, the hull utilizes materials adapted to tropical climates and saline waters. Internal features include air conditioning, expanded living quarters, individual bunk beds to eliminate hot-bunking, and dedicated facilities for female personnel. For propulsion, the class uses an X-shaped rudder configuration to assist maneuverability in shallow waters, combined with a fuel-cell air-independent propulsion (AIP) system that charges lithium-ion batteries to extend underwater endurance.

The armament consists of forward-firing torpedo tubes capable of launching heavyweight torpedoes, anti-ship missiles, and naval mines. The design features a Horizontal Multi-Purpose Airlock for deploying special forces or weapons, with an option to integrate a Vertical Multi-Purpose Airlock. The Black Shark Advanced heavyweight torpedo is integrated into the weapon systems. Sensor and command integration includes a Combat Management System developed by Atlas Elektronik and ST Electronics, alongside DSTA-developed data analytics and decision support engines. Automation reduces the required crew complement, allowing the vessel to be operated on a three-shift rotation.

Construction of the lead submarine, Invincible, began in Kiel, Germany, in 2014, and the vessel was launched on 18 February 2019. Delivery was delayed to 2022 due to pandemic-related restrictions. The second and third vessels, Impeccable and Illustrious, were launched on 13 December 2022. In mid-2023, Impeccable was transported to Singapore on the heavy-lift ship Rolldock Storm to begin local sea trials. The fourth vessel, Inimitable, was launched in April 2024. Invincible and Impeccable entered active service on 24 September 2024. Invincible is utilized for crew training, while Impeccable and Illustrious have undergone local sea trials to achieve operationalisation. Illustrious and Inimitable are launched, with commissioning scheduled for 2028.