PEARL HARBOR, Hawaii — The U.S. Navy is spending more than $20 million each year sending ships to poorer nations in the Asian-Pacific region to provide cataract surgery, dental fillings, and other medical care.

The Navy and its sailors are more often recognized for sending aircraft carriers to help troops in Afghanistan, fighting pirates off the Somali coast, or intercepting ballistic missiles in missile defense tests off Hawaii. But the U.S. Pacific Fleet and analysts say the humanitarian missions are key to promoting U.S. national security, with relatively low costs even during a time of shrinking budgets.

Adm. Cecil Haney, commander of the U.S. Pacific Fleet, said the missions strengthen relationships with other countries.

"You’re building trust, bonds, and how to communicate," Haney said in an interview at his Pearl Harbor headquarters. "We give it a fancy term, interoperability — it’s more than just technology. It’s cultural. It’s this business of building trust with like-minded nations."

Haney spoke shortly after the hospital ship USNS Mercy and its 1,200-member crew stopped in Pearl Harbor on its way back to San Diego following a five-month-long tour of Cambodia, Indonesia, the Philippines, and Vietnam.

The ship spent two weeks in each country. During its most recent tour, medical personnel from 13 other countries — from Japan to Malaysia — came aboard to help out, along with 28 non-governmental organizations from the United States and other countries.

Capt. William Cogar, the Mercy’s executive officer, said the ship faced particularly high demand for cataract surgery, even from patients in their 30s and 40s. Many people in the countries visited don’t wear sunglasses, he said.

"Now they can see again," Cogar said.

Animals — including livestock such as water buffalo and pigs — were also treated by veterinarians on board.

Abe Denmark, senior director of the National Bureau of Asian Research, an independent, non-partisan think tank, said the missions help people develop a better opinion of the United States.

"The image of American power going abroad and bringing benefits to people all around the world who otherwise wouldn’t have access to this kind of care — to this kind technology — it builds the image of American power, of American soft power, in a way that’s almost unquantifiable," Denmark said.

The U.S. learned the public relations value of such deployments when the U.S. Pacific Command sent ships and planes to deliver food, tents, and medical care for victims of the 2004 Indian Ocean earthquake and tsunami.

U.S. approval ratings in Indonesia, which is predominantly Muslim, climbed to 38 percent in 2005 from 15 percent two years earlier because of the help, according to a poll by the Pew Global Attitudes Project.

The Navy started sending hospital ships and other Navy vessels on annual humanitarian tours shortly afterward. The program — called Pacific Partnership — is now in its eighth year.

Unlike several decades ago, the Navy isn’t focused on defeating the Soviet threat. It can make something like humanitarian aid an important part of its overall strategy. Population growth and other demographic change in the Asia-Pacific have also created more demand for humanitarian assistance, he said.

Seth Cropsey, a senior fellow at the Hudson Institute, said the aid will likely continue even as budgets tighten. The cost is low, Cropsey said, compared with the $16 billion a year the Navy spends building ships.

"It’s a good deed, and people are grateful for it as well they should be," Cropsey said. "No one loses."