The last of Singapore's most advanced submarines was declared battle-ready on Tuesday, sharpening the capabilities of the Republic of Singapore Navy (RSN) in underwater warfare.

The RSS Swordsman was commissioned, following more than two years of tests and torpedo-firing exercises in Sweden and in the warmer and more corrosive waters here. The 60.5m diesel-electric vessel arrived in Singapore in last December. This is the second Archer-class vessel to be added to the RSN's 171 Squadron, after the first, RSS Archer, was declared operational in 2011. The submarine squadron also comprises four ageing Challenger-class submarines.

Deputy Prime Minister Tharman Shanmugaratnam, who was at the ceremony in Changi Naval Base, said the new vessel will strengthen the navy's ability to safeguard Singapore's "continued and unimpeded access to the maritime routes".

He noted that Tuesday's ceremony also marked the end of the RSN's eight year journey to replace some of the Challenger-class submarines, which were built in the 1960s.