Patrick Semansky/AP Photo

ANNAPOLIS, Md. - Defense Secretary Leon Panetta told a graduating class of naval officers today that rapidly changing global challenges for the United States meant they would be tasked with leading a military in metamorphosis.

"You must be prepared to respond to whatever threats we confront in the future with courage, with creativity and with leadership," Panetta said, "Adapting to new challenges is what the naval service does best. This is not a time for playing it safe. It's a time for imagination, a time for initiative."

He made the remarks to 1,099 graduates of the U.S. Naval Academy at Annapolis. The ensigns and second-lieutenants-to-be, sitting in full dress uniform under a blazing sun, were warned of the dangers they would face.

Panetta told the graduates the threat of a nuclear North Korea and Iran, cybersecurity, the rising prominence of the Asia-Pacific, and the ongoing pursuit of terrorism were reminders that "we are still at war."

"All of this coming at a time of increasing budget challenges here at home," said Panetta.  "Our nation now looks to you, the next generation of military leaders, to confront the challenges I just outlined."

Panetta touted NATO's success in Libya and America's commitment to a 2014 drawdown in Afghanistan. He told the students that strengthening ties with China would be "key" to peace from the Pacific to South Asia.

"That reality is inescapable for our country and for our military," he said.

As the military's strategies evolve, so do the very makeup of its members, said the secretary.

"You are men and women from every state in the union and 12 foreign nations; rich and poor; secular and religious; black, white, Latino, Native American, Asian; straight and gay."

Some of 2012's crop of military officers will be the first to enter a the service as openly gay service members, eight months after the repeal of the military's "Don't Ask, Don't Tell" policy.

This Annapolis class even witnessed the graduation of its first paraplegic student, 22-year-old Kevin Hillery. He was paralyzed from the waist in an accident during his junior year, but was allowed to remain at the academy to finish his classes.

Panetta said the diversity of the class served as a tribute to the first African American graduate of the war college, Lieutenant Commander Wesley Brown. Brown, a member of the class of 1949, died last week.

Secretary of the Navy Ray Mabus introduced Panetta at today's ceremonies. Maryland Gov. Martin O'Malley and Rep. Robb Wittman, R-Va., were also in attendance.

Panetta's appearance at Annapolis means a member of the administration has now officiated at each of the major military academies' graduation ceremonies this year. In the last month President Obama has spoken at the Air Force Academy in Colorado, Vice President Biden at West Point, and Homeland Security Secretary Janet Napolitano at the Coast Guard school in Connecticut.