WASHINGTON - Defense Secretary Robert Gates on Monday said new weapons threatened US dominance of the high seas and questioned the US Navy's reliance on costly aircraft carriers and submarines.

Anti-ship missiles and stealthy submarines could undermine the US military's global reach, putting carriers and American subs at risk, Gates said in a speech to retired members of the US Navy.

"We know other nations are working on asymmetric ways to thwart the reach and striking power of the US battle fleet," Gates said.

He cited the Lebanese Shiite militia Hezbollah, which had used anti-ship missiles against Israel in 2006, and Iran's arsenal of missiles, mines and speedboats that he said were designed "to challenge our naval power in that region."

The US military's "virtual monopoly" in precision guided weapons was "eroding" and the spread of missiles jeopardized Washington's means of "projecting power," he said.

More sophisticated submarines -- that are more difficult to track -- along with other underwater weapons "could end the operational sanctuary our navy has enjoyed in the Western Pacific for the better part of six decades."

The new "anti-access" weapons could potentially render America's costliest vessels obsolete, with vast sums of money devoted to "wasting assets," he said.

"Our navy has to be designed for new challenges, new technologies, and new missions -- because another one of history's hard lessons is that, when it comes to military capabilities, those who fail to adapt often fail to survive," he said.

With the United States fleet of attack submarines and warships far exceeding any other country, Gates questioned if it was wise to spend billions more on the same programs given the changing strategic landscape.

"At the end of the day, we have to ask whether the nation can really afford a navy that relies on three- to six-billion-dollar destroyers, seven-billion-dollar submarines and 11-billion-dollar carriers."

To reduce a dependence on carriers and regional bases, naval commanders will need to develop ways to strike at longer range with the help of robotic, unmanned aircraft as well as smaller subs and unmanned underwater vessels, he said.

It was a blunt message from Gates, who has not shied away from cutting some big weapons programs with roots in the Cold War, including the F-22 fighter jet.

For the past year Gates has argued that defense spending should be based on "realistic" threats and reflect what troops in Iraq and Afghanistan need, pushing for more helicopters and unmanned planes while cutting back some high-priced conventional weapons projects.

New technology as well as budget pressures will force future leaders of the navy and the US Marine Corps to take a second look at long-held assumptions about US military power, he warned.

"Do we really need 11 carrier strike groups for another 30 years when no other country has more than one? Any future plans must address these realities."

He cited his approval of funds for ships designed for shallow water, as smaller vessels had become vital for special operations against insurgents and Islamist extremists.

"As we learned last year, you don't necessarily need a billion-dollar guided missile destroyer to chase down and deal with a bunch of teenage pirates wielding AK-47s and RPGs (rocket-propelled grenades)," he said.

He also cast doubt on the need to invest in new vehicles for major amphibious landings, suggesting such operations were unlikely and that increasingly advanced anti-ship weapons would require ships to launch at a greater distance from the shore.

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