US Defense Secretary Chuck Hagel Sunday visited the US Navy's Littoral Combat Ship deployed in Singapore, a symbol of Washington's strategic "pivot" towards Asia.

The LCS is designed as the navy's ultimate multitasking vessel despite significant development problems.

The USS Freedom, the first of 52 LCS vessels which the navy plans to build at a total cost of $37 billion, arrived in mid-April in Singapore for its first deployment.

Four LCS, which are designed to operate close to shore, will eventually be forward-deployed at the city-state's Changi naval base as part of Washington's military "rebalancing" towards the Asia-Pacific.

The aim is to increase the US military presence in the region by avoiding a two-week voyage from the US west coast before deployment.

Hagel gave the deployment his strong backing in remarks to the crew from the Freedom's bridge.

"You're making history out here," he told them. "What you represent to our partnerships in the Asia-Pacific can't be overstated."

The 120-metre (396-foot) USS Freedom is a whole new type of ship. Like a Lego model, it can be adapted for specific missions through a system of interchangeable modules and crew.

"We see it as like a truck, you can put different things inside," said its captain, Lieutenant Commander Clayton Doss.

The ship currently has a "surface combat" module including a helicopter, two 30 mm cannon and two powerful Zodiac speedboats for its Southeast Asian role.

The deployment of the USS Freedom came at a time of heightened tensions on the Korean Peninsula and as China publicly flexed its naval muscle in the South China Sea, where it has competing territorial claims with some Southeast Asian states.

There are also still cases of piracy in the Strait of Malacca.

Out of the hundred-strong crew, 38 of them are dedicated to the surface combat module. They will be replaced by others if the ship is reconfigured for an anti-submarine or anti-mine role, said Doss. Replacing one module with another takes no longer than 96 hours, he said.

The aim of the design is to keep the ship light and speedy -- the LCS can sail at more than 40 knots -- and avoid having to carry equipment and crew to perform different tasks.

"The other reason that modularity is so helpful is that it's very hard to know what types of combat systems you need to deal with the challenges in the future," Doss said.

"We have three mission packages now, it doesn't mean those are the only three, we'll continue to create new ones."

The US Navy believes so strongly in the concept that the LCS ships, of two different classes, will eventually make up almost 20 percent of its entire fleet.

Apart from the four to be berthed in Singapore, eight others are expected to be based in Bahrain.

But the programme has suffered some troubling teething problems.

"The LCS program has become controversial due to cost inflation, design and construction issues with the lead ships built to each design, concerns over the ships' ability to withstand battle damage, and concerns over whether the ships are sufficiently armed," said a Congressional Research Service report in April.

After about 30 months of operations, the Navy discovered cracks in the superstructure and hull of one ship along with corrosion.

Doss said the problems were being solved.

"We will come across problems and we will make discoveries before it (LCS) enters the fleet in full operational capability," Vice-Admiral Allen Myers, deputy Chief of Naval Operations, said last month.