RSS Invincible

The customised design is oceangoing and larger than the Challenger and Archer-class submarines operated by the Singapore Navy. The design is expected to be influenced by the export Type 214 submarine or Type 216 submarine, which have been designed for the potential needs of several other navies (Australian, Canadian and Indian).[2][3] Features will include AIP and a combat system designed by both Atlas Elektronik and ST Electronics. The Invincible class also features an "X" rudder "which offers enhanced manoeuvrability in confined littoral waters, as opposed to the Type 214's cruciform rudder arrangement.

Type 218SG Republic of Singapore Navy Invincible-class submarine rendering.

The X rudder is used on the Type 212 submarine and its larger and newer derivative, the Dolphin 2-class submarine built for the Israeli Navy which is almost identical in size to the Invincible-class submarine (Israel and Singapore have deep military ties and frequently procure the same weapon systems across their military platforms).

The subs are believed to have Horizontal Multi-Purpose Airlock, which can be used to launch either torpedoes, divers, or special forces assault teams, and also have the capability to launch cruise-missiles while submerged[4] with an option for Vertical Multi-Purpose Airlock, for launching missile vertically, like the Tomahawk , Blue Spear or Naval Strike Missile[5]