# Invincible-class submarine

The Invincible-class submarines, formally classified as the Type 218SG submarines, is a class of conventionally-powered attack submarines on order by the Republic of Singapore Navy (RSN) from German-based naval conglomerate ThyssenKrupp Marine Systems (TKMS). Tailored to the operational requirements of the RSN, the model is derivative of the export-oriented Type 214 submarine, with specific design characteristics drawn from Type 212 submarines. They feature several capabilities, including a substantial level of automation, a significant payload capacity, enhanced underwater endurance and superlative ergonomics.
Singapore's Ministry of Defense (MINDEF) ordered a total of four Type 218SG submarines, of which two were ordered in 2013 and two more in 2017, as a replacement to the RSN's existing Challenger-class and Archer-class submarines. Having been built and launched between 2019 and 2024, the class comprises four submarines, namely, the Invincible, the Impeccable, the Illustrious and the Inimitable; of the four, the first is currently utilized for the training of the RSN's submariners, while the second and third are undergoing local sea trials aimed at achieving operationalization. The RSN plans to have all four submarines in active service by 2024.

## Design
### Development

The design of the Type 218SG was jointly created by Defence Science and Technology Agency (DSTA), ThyssenKrupp Marine Systems (TKMS) and the Republic of Singapore Navy (RSN). The design of the submarines is highly customised—conceived to fulfill specific naval requirements of the RSN—including naval operations in littoral waters, guarding sea lines of communication (SLOC), intelligence-gathering (ISTAR) and special operations. The design is believed to be based on the Type 214 export-centric submarine, with design inferences from the Type 212 submarine—both of which were designed by TKMS. The design of the Type 218SG is also believed to have been influenced by the Type 216 submarine concept.
The Type 218SG has a length of 70 metres (229 ft 8 in) and a beam of 6.3 metres (20 ft 8 in), with an overall displacement of about 2,000 t when surfaced and 2,200 t while submerged. It has an estimated speed of about 10 knots (19 km/h; 12 mph) while surfaced and 15 knots (28 km/h; 17 mph) while submerged.

### Features

The Type 218SG features several unique characteristics, such as:
* An X-shaped rudder configuration similar to that on the Type 212 submarines, Dolphin-class and the Dakar-class submarine of the Israeli Navy, for better maneuverability in Singapore's busy but shallow littoral waters around the Straits of Malacca and the South China Sea—as opposed to the Type 214's cruciform rudder configuration.
* A fuel-cell powered air independent propulsion (AIP) module for charging lithium-ion batteries (LiB) which allows it to remain submerged for about 50% longer than the Archer-class submarines; several estimates put the Type 218SG's underwater endurance at about 28–42 days (4–6 weeks), without snorkelling.
* A Horizontal Multi-Purpose Airlock (HMPL)—which can be utilised to launch torpedoes, special operations forces, divers and submarine-launched cruise missiles (SLCM); the submarines also come with an option to integrate a "Vertical Multi-Purpose Airlock" (VMPL), for launching missiles vertically, similar to a Vertical Launching System module.
* Use of extensive ergonomical factors for crew comfort—such as air conditioning, enlarged living quarters, additional showering facilities, individual on-sharing bunk beds, personal media entertainment systems (similar to those in commercial airlines) toilet cubicles, additional storage space and equipment unique to the physiques of the RSN's sailors.
* Extensive features of automation—"Combat Management System" (CMS) jointly developed by Atlas Elektronik and ST Electronics and data analytics/decision-support engines developed by the DSTA - which allows the crew to operate the submarine on three 8-hour shifts, instead of two 12-hour shifts, thus allowing greater periods of rest during protracted underwater deployments. The high-level of automation also reduces the crew complement from the usual 35 to just 28 (fewer than other contemporary conventional submarines), of which around 10 are on active duty at any-one time, with the other 18 off-duty or resting.
* Utility of specific materials accustomed to Singapore's tropical climate and saline waters.
* A higher payload carrying capacity and greater firepower than the Challenger-class and Archer-class submarines, owing to its larger size.
* Separate accommodation for special forces team and equipment.

## Instrumentation
### Armament

Current details about the Type 218SG's armament are scant and almost non-existent; however, it is understood that the submarine features eight 533-millimetre (21.0 in) and two 650-millimetre (26 in) forward-firing torpedo tubes— (same configuration with Israel's Dolphin-II submarines) which may be used for firing heavyweight torpedoes, anti-ship missiles and for laying naval mines, as well as a dedicated horizontal air-lock, to disembark naval special forces teams.
The Type 218SG is reported to have a greater ordnance payload (and essentially greater firepower) than the RSN's previous submarines, owing to its much larger size.

### Sensors

Not much about the Type 218SG's sensors and automation have ever been reported by Singapore; however, it is understood the submarines are equipped with a "Combat Management System" (CMS) jointly developed by German-based Atlas Elektronik and Singapore-based ST Electronics, along with data analytics and decision support engines developed by the DSTA.
The high levels of sophisticated automation and decision-making systems allows the submarines to run on three 8-hour shifts (instead of two 12-hour shifts), thus allowing the crew more rest to endure prolonged underwater missions. Unlike most submariners, crew of the submarines do not share their beds "hot-bunking" with others, except when a naval special forces detachment is onboard, also a similar arrangement found on the Israeli Navy's Dolphin-II class submarines.
Given its sophisticated automation, each submarine is crewed by only twenty-eight sailors—a number similar to the RSN's other smaller submarines, but fewer than other contemporary conventional submarines.

## History
### Purchase of four submarines

In November 2013, Singapore's Ministry of Defense (MINDEF) selected the Type 218SG design, offered by TKMS, as a replacement to the RSN's existing submarine fleet, siding an offer of three conventionally-powered submarines (presumably the Scorpène-class submarine) from French-based naval conglomerate Direction des Constructions Navales (now Naval Group). On 29 November 2013, MINDEF officially contracted TKMS to supply two Type 218SG submarines, along with a training and logistics package, at an estimated cost of US$1.36 billion. The order for the two submarines bore noteworthy significance for being the RSN's first-ever order for new custom-built submarines, since the service had previously relied on the acquisitions of the second-hand Challenger-class and the Archer-class submarines. The purchase of the two submarines was officially announced on 2 December 2013. According to the terms of the contract, the two submarines were initially scheduled to be delivered between 2020 and 2021.
On 16 May 2017, Singapore's minister of defence Ng Eng Hen announced that the RSN had placed an additional order for two more Type 218SG submarines, with additional arrangements of logistics and crew-training, bringing the total number of its ordered submarines to four. According to the terms of the contract, the two additional submarines are to be delivered between 2024 and 2025. In January 2023, it was reported that the cost of the purchase would be USD$1.8 billion.

### Fifth submarine rumours

In December 2021, German news outlet Der Spiegel reported that the German government, headed by then-outgoing chancellor Angela Merkel, had sanctioned a series of last-minute arms deals, including the export of an additional Type 218SG to Singapore.
Nevertheless, the authenticity of the deal is yet to be verified by the RSN and TKMS. Singapore has neither confirmed nor denied the existence of a fifth Invincible-class submarine.

### Construction

The construction of the first submarine began in 2014, with a steel cutting ceremony at TKMS's shipyard in Kiel, Germany. The first submarine, christened as the Invincible, was launched in an elaborate ceremony on 18 February 2019, with defense minister Ng Eng Hen and representatives of the RSN in attendance. During the ceremony, Ng revealed the names of the other three submarines, namely, Impeccable, Illustrious and Inimitable. Invincible began its initial sea trials in September 2020, with its planned delivery date scheduled for 2020. However, in June 2020, Ng announced that the delivery of Invincible had been postponed to 2022, owing to restrictions caused by the COVID-19 pandemic.
The construction of the second ordered batch began in January 2018, commencing with the steel-cutting ceremony of the third submarine, Illustrious, which was attended by representatives from TKMS and the DSTA.
In April 2021, German news outlet Lübecker Nachrichten reported that a Type 218SG submarine, presumably either the Invincible or the Impeccable, had suffered fire outbreak during its sea trials. Nevertheless, the submarine in question wasn't reported to have been seriously damaged, nor were the crew reported to have sustained injuries.
One year later, in November 2022, during a one-day visit by German chancellor Olaf Scholz to Singapore, Singaporean prime minister Lee Hsien Loong announced that the second and third submarines of the class, namely, the Impeccable and the Illustrious, would be launched in December of that year. The two boats were launched in an elaborate launching ceremony at TKMS's Kiel shipyard on 13 December, which was attended by Lee, Scholz and Singaporean minister of foreign affairs Vivian Balakrishnan.
In May 2023, Impeccable, which had completed its sea trials earlier that year, was loaded onto a heavy-lift transport ship, the Rolldock Storm, for the transit trip to Singapore. Departing Kiel on 1 June, the Rolldock Storm undertook a one-month voyage, arriving in Singapore on 7 July, where it was unloaded the day after. Later that month, MINDEF announced that Impeccable would undergo a new set of local sea trials and workup aimed at achieving operationalization prior to its commissioning later in the year. The final boat, the Inimitable, was launched by Singapore's Senior Minister and Coordinating Minister for National Security Teo Chee Hean in April 2024.

### Additional purchase of two submarines

In March 2025, Defence Minister Ng Eng Hen announced a plan for the Singapore Armed Forces to purchase 2 additional Invincible-Class submarines, bringing the total number of submarines purchased to six, up from four previously.

## Ships in class

| Name | Builder | Launched | Commissioned | Status |
| RSS Invincible | Germany ThyssenKrupp Marine Systems (TKMS) | 18 February 2019 | 24 September 2024 | Active. |
| RSS Impeccable | Germany ThyssenKrupp Marine Systems (TKMS) | 13 December 2022 | 24 September 2024 | Active |
| RSS Illustrious | Germany ThyssenKrupp Marine Systems (TKMS) | 13 December 2022 | 2023 (Scheduled) | Launched |
| RSS Inimitable | Germany ThyssenKrupp Marine Systems (TKMS) | 22 April 2024 | 2024 (Scheduled) | Launched Christened in April 2024. |