GRAND FORKS AIR FORCE BASE, N.D. — The Air Force's top officer said the service is critically short of personnel and needs to expand by more than 30,000 active duty servicemembers to meet its security obligations, including an air war against Islamic State militants.

"We just got too small too fast and we've got to grow," Gen. David Goldfein, the Air Force chief of staff, told USA TODAY in an interview Wednesday. "We're at a risk level I'm not comfortable with."

Goldfein, who is completing a five-day tour of air bases around the country, said the trip reinforced his concerns that the service is stretched thin. "The shortage of people has fundamentally changed the way we do business," he said. "To most of the American people they still think they have the Air Force of Desert Storm (1990-91 Gulf War) and we're not even close."

President-elect Trump, who promised to rebuild the military, will likely face an array of requests from the services, which have lobbied for more troops and weapons in years past but have had to preside over smaller forces more recently because of budget pressures despite a resurgence of new threats, particularly in the Middle East.

Goldfein said he will recommend expanding the size of the active duty Air Force from its current size of about 317,000 to 350,000. It would probably take five or six years to reach the higher level. Under current plans, the Air Force had planned to grow to 321,000.

It was not immediately clear what impact the expansion would have on the service's $120.4 billion budget.

The U.S. military withdrew from Iraq in 2011 and has reduced the size of its force in Afghanistan to less than 10,000.

In 2014, however, the Islamic State swept into Iraq and other parts of the Middle East, prompting the Obama administration to deploy roughly 5,000 troops in Iraq and begin a bombing campaign over Iraq and Syria. U.S. aircraft have dropped thousands of munitions targeting the Islamic State in both countries.

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The Air Force is ferrying tons of weapons and ammunition to Iraqi forces battling the Islamic State, and has air-dropped supplies to a rebel force marching on Raqqa, the Islamic State's de facto capital in Syria. It is also responding to other global crises.

"It seems like every two weeks we're responding to a crisis or event around the globe," said Gen. Carlton Everhart, commander of the Air Mobility Command at Scott Air Force Base in Illinois.

Meanwhile, Russia and China are emerging as potential threats that could challenge the U.S. military in ways the Islamic State has not. China is expanding its presence in the South China Sea and Russia has become a major player in Syria's civil war, siding with the regime of President Bashar Assad.

The U.S. Air Force has rarely been challenged in the skies during its campaign against the Islamic State. That could change if the United States were to face another nation's military capable of challenging the U.S. military's technological advantages.

Earlier this week, Goldfein spent a night with a crew in an underground nuclear control facility in a remote windswept corner of Nebraska. Airmen guard the facility round the clock and a pair of young officers sit at the controls that would launch nuclear-tipped Minuteman III missiles from nearby silos if the president orders strikes.

At Schriever Air Force Base in Colorado, he spoke to airmen manning 24/7 operations centers where the service controls satellites that provide GPS and communications coverage around the world.