The RSS Chieftain, an Ex-Sjoormen class submarine, was turned over to Singapore's Minister of State for Defence David Lim at the Kockums Shipyard in Kariskrona, Sweden.

A defence ministry statement said the submarine will undergo a series of tests to ensure it can operate in tropical waters before it sails to Singapore at the end of the year for commissioning into the naval fleet.

The RSS chieftain is the last of four submarines ordered by Singapore, but so far, only one, the RSS Conqueror, has been commissioned after undergoing sea trials and torpedo firing tests.

The other two, RSS Challenger and RSS Centurion, also made in Sweden, have yet to be brought to Singapore.

The small and stable island republic lies in the heart of politically troubled Southeast Asia, and at the mouth of the strategic Straits of Malacca, one of the world's busiest shipping lanes.

"Singapore depends on the sea for a significant part of our prosperity, because of the importance of maritime trade to our economy," Lim said at the turnover ceremonies May 22.

"We therefore attach great importance to the task of building a modern and balanced navy to ensure that the sealines of communications are free and safe for navigation," he said in a speech, copies of which were released here.

Singapore also has one of the region's best equipped armies and air force.