The hospital ship USNS Mercy was the latest ship to deploy, setting sail late Wednesday from San Diego, California to join the relief operation that already involves 17 US Navy ships, nearly 50 helicopters and 28 military transport planes.

"Preliminary estimates of the cost to date in support of the tsunami relief operations is approximately 40 million," said Lieutenant Commander Greg Hicks.

He said the military is spending about five to six million dollars a day, including about 2.4 million dollars for the more than 13,000 military personnel in the region and 3.2 million dollars to operate the ships and planes deployed so far.

"I imagine the cost will go up as we flow more forces into the theater," said Hicks.

The Mercy, which last deployed in 1990 for the Gulf War, is equipped with 250 beds but can be expanded to 1,000 beds.

Admiral Thomas Fargo, commander of US forces in the Pacific, said this week that the Pentagon was looking to staff it with medical personnel and humanitarian relief workers from non-governmental organizations.

A spokesman for the US Pacific Command said planning for the use of the ship was still going on with a role for non-military relief organizations still among the options.

The ship is expected to take two to three weeks to reach the region.

Two container ships, each with a capacity to store up to 90,000 gallons of fresh water, arrived in the region Wednesday and Thursday, sailing through the Straits of Malacca, said Navy Captain Rodger Welch, the Pacific Command spokesman.

The ships, which carry prepositioned military supplies, were the first of six that will be moving into the area from northeast Asia over the next few days.

Their capacity to distill and store fresh water will help authorities meet a crucial need and help stave off disease in areas devastated by the December 26 tsunami.

An armada led by the aircraft carrier USS Abraham Lincoln and the helicopter carrier USS Bonhomme Richard has been pivotal in moving supplies by helicopters to outlying areas. A fleet of 18 C-130 aircraft also have been active within the theater.

Welch said long haul C-17 and C-5 transport planes are now able to get into the airport at Medan, a logistics hub on the Indonesian island of Sumatra, which should help accelerate the flow of relief supplies.

With the arrival of air controllers, US military pilots have been able to make use of the better organized airspace to fly more night missions, he said.

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