that the project would cost about one billion Euros and take six years to complete, with the first submarine expected to be delivered in 2020. The diesel electric submarines will have 50 per cent longer endurance, more firepower, more capable sensors and advanced automation than the existing fleet of RSN submarines. Armed with eight torpedo tubes and manned by a crew of 28, they can travel at a surface speed of more than 10 knots and a submerged speed of more than 15 knots. These submarines are particularly customized for Singapore's shallow and busy waters. The first of four, RSS Invincible, was launched on 18 February 2019. She will undergo sea trials in Germany before delivery in 2022. The second and third boat, RSS Impeccable and RSS Illustrious were launched on 13 December 2022, expected to be delivered in 2023. The remaining one is scheduled to follow by 2024. The Invincible and Archer-class submarines are projected to replace the Challenger-class afterwards. All submarines, regardless of class, form the Seventh Flotilla of the RSN. The RSN also operates the submarine support and rescue vessel . Corvettes In 1983, the RSN ordered six corvettes from Friedrich Lürssen Werft of Germany, with the first being built in Germany and remaining five locally by ST Marine. The corvettes represented a strategic change in Singapore's defence posture as the Navy sought to redefine its purpose to be "more than a coastguard" and project power in the region for deterrence purposes; they were the first ships in the RSN to have an anti-submarine capability, and remain the fastest ships in the fleet with a speed in excess of 30 knots. A244-S torpedoes were reportedly acquired to counter the threat of an increased number of submarines passing through the Malacca Strait, with Soviet submarines having been tracked passing through entirely submerged. The first three ships were commissioned in August 1990 and the remaining three in May 1991. The corvettes have been continuously upgraded to incorporate new technologies and better sea keeping capabilities. Two sets of 8-cell Barak I were installed in 1996 as part of a general refit. A life extension program between 2009 and 2013 redesigned the mast to incorporate new sensors, overhauled the combat management system, and added the ability for the ship to launch a single ScanEagle UAV for remote surveillance without the need to approach a target. The anti-submarine torpedoes and variable depth