Backed by an array of US warships, planes and helicopters, more than 13,000 US military personnel have been dispatched to help Indonesia, Thailand and Sri Lanka, the countries most affected by the December 26 disaster.
Conducting its largest operation in Asia since the Vietnam War, the US military could remain in the region for up to six months, analysts said here Tuesday.
The mammoth humanitarian effort would ease concerns among Asian governments suspicious over American military ambitions and help gain their backing in the US-led "war on terror," they added.
"It's pretty impressive what the Americans are able to do with their military and if handled appropriately and carefully, it could lead to a better, more cooperative military relationship with the region," said Robert Sutter, visiting professor of Asian studies at Georgetown University.
"The message that hopefully is getting across is that Americans are not just out blasting terrorists. They are people with concerns and can help in a military way," he said.
Before the tsunami disaster it would have been unthinkable for a US aircraft carrier to dock in Indonesia's waters, or US Marines to rub shoulders with troops from the world's most populous Muslim nation.
Washington had banned key military cooperation with Indonesia because of human rights disputes, but the disaster has now brought the armed forces of both countries together in a major relief operation.
The USS Abraham Lincoln, an aircraft carrier with 6,000 sailors on board, is currently stationed about 28 kilometres (15 nautical miles) off Indonesia's Aceh province providing aid and sending ashore medical teams.
A fleet of Sea Hawk helicopters from the Abraham Lincoln has also been flying food, water and medical supplies into Aceh, where until the tsunami most foreigners were barred because of Indonesian fears about possible outside aid to rebels waging an independence struggle.
US Rear Admiral Doug Crowder told the Washington Post he expected the joint efforts to improve prospects for resuming full military ties with Indonesia.
The government of President George W. Bush has sought to restore military links, in large part to help fight terrorism, but the US Congress has repeatedly blocked the effort.
"This relief effort demonstrates there could be greater military cooperation with Indonesia," said Dana Dillon, an analyst with the conservative Heritage Foundation.
US marines arrived in Sri Lanka on Tuesday for a deployment that will eventually total 1,500 troops -- reportedly much to the chagrin of giant neighbour India, suspicious of US military intentions.
"Sri Lanka had been seeking US military aid for some time because of an ongoing civil war with the Tamil Tigers, but the American side had been reluctant," noted Dillon.
Part of Sri Lanka's tsunami devastated areas are controlled by the rebel Liberation Tigers of Tamil Eelam (LTTE), which Washington has designated a terrorist group.
US forces are also using Thailand's Vietnam war-era air base of Utapao as an airlift hub for the humanitarian mission in the region, strengthening potential US military logistical support throughout southeast Asia.
Thailand and the Philippines are key US military allies in the region. Singapore hosts a permanent site for US navy ships to dock for maintenance, repairs, supplies, and rest and recreation for the crew.
But the United States has been unable to expand its military influence in the region largely due to suspicions by Indonesia and Malaysia.
The two countries have opposed an American plan to tighten security in the vital Malacca Straits shipping lanes, which might have involved elite US troops stationed nearby.
Derek Mitchell of the Center for Strategic and International Studies, a Washington-based think tank, said the tsunami disaster underlined the importance of US military presence in the region.
He cited particularly the American military base in Okinawa, from where resources were tapped rapidly for the humanitarian effort.
"The United States has this unique capability to move rapidly with its military to take care of humanitarian and other security challenges in Asia," Mitchell said.
"In the absence of this capability which isn't nearly there in Asia, the United States plays this indispensable role."
