SINGAPORE - Singapore commissioned two new advanced submarines on Tuesday, vessels its navy says are meant to protect sea lines of communication, and which experts said would range beyond the waters of the tiny city-state to keep tabs on the region.

The country's fifth and sixth submarines, the Invincible and the Impeccable, were ordered from Germany's ThyssenKrupp Marine Systems in 2013 in a 1-billion-euro deal, and join older Archer- and Challenger-class boats.

They represent a technological step forward for Singapore's fleet, experts say, allowing the wealthy Southeast Asian nation to operate farther from shore using fewer sailors, and making its craft among the quietest in the region.

"They are an excellent force multiplier," said Colonel Fong Chi Onn, commander of Singapore's submarine flotilla. "And for a country as small as ours, we need all the force multipliers we can get."

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The two new Invincible-class submarines were moored at adjoining piers, decked in colorful naval pennants, with their X-shaped rudders peeking from the water, for Tuesday's event at Changi Naval Base.

Prime Minister Lawrence Wong commissioned the vessels in a ceremony watched by their crew and military dignitaries in white dress uniforms gathered along with their families.

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The Invincible class needs a complement of just 28 for each 70-metre (230 ft), 2,200-ton submarine, and crew said on Tuesday that automation of time-consuming tasks made operations easier. They are also Singapore's first submarines with crew facilities for women, and both have female officers.