The Pearl Harbor guided missile destroyer USS Russell and more than 270 of its crew left Hawai'i on Jan. 5 for the Middle East and Western Pacific.

This after the Russell returned two months earlier from a three-month deployment to the Western Pacific. In between, there were repairs and training.

The U.S. Navy continues to be high in demand in the Pacific and Atlantic — now for different reasons than its former Cold War posture — and that has brought new wear and tear for sailors and ships.

"Over the past decade, we have seen a decline in the number of ships in our inventory," said Adm. Patrick Walsh, commander of U.S. Pacific Fleet. "However, the demand signal for those assets has steadily increased to support efforts in Iraq and Afghanistan, counter piracy around the Horn of Africa, assist with security requirements in the European theater, and respond to humanitarian crisis about every 60 days, on average."

The Navy has 287 deployable ships. Now 49 percent are under way and 40 percent are on deployment. In the early 1990s, a typical day in the Navy saw 25 to 30 percent of the fleet under way or deployed.

Walsh said the current usage level "is not a sustainable model." The Navy is trying to get to 313 ships.

Twenty U.S. ships have ballistic missile defense capability, including six cruisers and destroyers at Pearl Harbor. That ability is in demand with nations including North Korea and Iran testing long-range missiles.

"If we are asked to track submarines or ballistic missiles, I think that Russell sailors are prepared for any (tasking)," Russell commander Cmdr. Rodney M. Patton said before deploying.

The Pearl Harbor-based destroyer USS Chung-Hoon was sent to the South China Sea in March to protect the USNS Impeccable after the U.S. reported that five Chinese vessels harassed the U.S. ocean surveillance ship.

Pacific Fleet dispatched three ships to help in Haiti — the aircraft carrier Carl Vinson, and a cruiser and destroyer.

"We operate in a world that continues to demand more from the sea and, as a result, the U.S. Navy must remain forward and engaged to help save lives and protect vital security interests," Walsh said.

Jan van Tol, a senior fellow at the Center for Strategic and Budgetary Assessments and a retired Navy captain, noted that the 49 percent of ships under way doesn't mean they are all gone on traditional six-month deployments.

These days, some deployments are shorter. Van Tol also believes the fleet is not overstressed.

"In my view, the current deployment rate is sustainable for a long time to come — as long as the Navy provides sufficient maintenance funds to keep ship and aircraft material readiness at required levels," he said.