West Point, N.Y. - The Army must prepare itself for the complex threats it will face in the future, including terrorists seeking weapons of mass destruction, outlier nations capable of nuclear warfare and the modern militaries being assembled in Russia and China, Defense Secretary Robert Gates said Friday.

As a result of the last 10 years at war, West Point cadets are joining a force that is resilient but also stressed and tired, the pentagon chief said during what is expected to be his last address to the U.S. Military Academy at West Point, training ground for future Army officers. Today's Army is filled with soldiers who have had "little opportunity to do more than catch their breath and then get ready for the next deployment," Gates said.

Gates, who has said he will leave office this year, laid out his vision for the future of the Army as it regroups after a decade of long and repeated deployments to Iraq and Afghanistan.

The Army has made a painful war-driven transition from a force designed to face off against other large militaries to a more nimble service that trains other armies and takes on nation-building even as it hunts insurgents, Gates said. It must better prepare itself to continue to face such unconventional threats and unorthodox duties in the future, he said.

Gates has asked a lot of the nation's 1.1 million-strong ground force since he took over the top Pentagon job in December 2006. He came in facing an escalating war in Iraq that was requiring more forces. Over time he sent thousands more troops into Iraq to a peak of nearly 180,000 and was forced to extend soldiers' deployment tours from 12 months to 15 months.

As the Iraq war began to wind down, he and the Obama administration ordered another surge - this time into Afghanistan, where they are battling entrenched insurgencies in the south and east.

The strains have left the Army and its families battered, with increased suicide rates, stress disorders and a complex array of wounds and brain injuries.

Gates told the cadets that as the Army competes for money in the tightening economy, it must realize that high-end conflicts will mainly require Navy and Air Force engagements, not a head-on clash of big land forces. The Army must not lose its ability to wage the kind of irregular warfare it has honed on the battlefields of Iraq and Afghanistan, and be prepared to face off against insurgents, militia groups and rogue states.

Gates also warned the cadets that the U.S. so far has a perfect record of never accurately predicting what the next war will be. But one thing, he said, is certain.

Any future defense secretary who advises the president to again send a big American land army into Asia or into the Middle East or Africa should "have his head examined," Gates said.