EXCLUSIVE: It was just a few years ago, in March 2011, when a pair of U.S. Air Force B-1 bombers – during a harsh winter storm – took off from their base in South Dakota to fly across the world to launch the air campaign in Libya, only 16 hours after given the order.

Today, many in the Air Force are questioning whether a similar mission could still be accomplished, after years of budget cuts that have taken an undeniable toll. The U.S. Air Force is now short 4,000 airmen to maintain its fleet, short 700 pilots to fly them and short vital spare parts necessary to keep their jets in the air. The shortage is so dire that some have even been forced to scrounge for parts in a remote desert scrapheap known as “The Boneyard.”

“It's not only the personnel that are tired, it's the aircraft that are tired as well,” Master Sgt. Bruce Pfrommer, who has over two decades of experience in the Air Force working on B-1 bombers, told Fox News.

Fox News visited two U.S. Air Force bases – including South Dakota’s Ellsworth Air Force Base located 35 miles from Mount Rushmore, where Pfrommer is stationed – to see the resource problems first-hand, following an investigation into the state of U.S. Marine Corps aviation last month.

Many of the Airmen reported feeing “burnt out” and “exhausted” due to the current pace of operations, and limited resources to support them. During the visit to Ellsworth earlier this week, Fox News was told only about half of the 28th Bomb Wing’s fleet of bombers can fly.

“We have only 20 aircraft assigned on station currently. Out of those 20 only nine are flyable,” Pfrommer said.

“The [B-1] I worked on 20 years ago had 1,000 flight hours on it. Now we're looking at some of the airplanes out here that are pushing over 10,000 flight hours,” he said.

"In 10 years, we cut our flying program in half," said Capt. Elizabeth Jarding, a B-1 pilot at Ellsworth who returned home in January following a six-month deployment to the Middle East for the anti-ISIS campaign.

On an overcast day in the middle of May with temperatures hovering in the low 50’s, two B-1 bombers were supposed launch at 9:00 a.m. local time to fly nearly 1,000 miles south to White Sands Missile Range in New Mexico for a live-fire exercise.

On this day, though, only one of the two B-1s that taxied to the runway was able to take off and make the training mission on time. The other sat near the runway for two hours. It eventually took off but was unable to participate in the live-fire exercise and diverted to a different mission, its crew missing out on valuable training at White Sands.

A spare aircraft also was unable to get airborne.

When operating effectively, the B-1 can be one of the most lethal bombers in the U.S. military’s arsenal. Designed as a low-level deep strike penetrator to drop nuclear weapons on the Soviet Union in the early 1980s, the B-1 has evolved into a close-air support bomber. Flying for 10-12 hours at a time high above the battlefield, B-1’s can carry 50,000 pounds of weapons, mostly satellite-guided bombs.

“It can put a 2,000 pound weapon on a doorknob from 15 miles away in the dark of night, in the worst weather,” said Col. Gentry Boswell, commander of the 28th Bomb Wing at Ellsworth.

But only half of these supersonic bombers can actually fly right now.

“The jet is breaking more today than it did 20 years ago,” Pfrommer said.

The B-1 issues are a symptom of a broader resource decline. Since the end of the Gulf War, the U.S. Air Force has 30 percent fewer airmen, 40 percent fewer aircraft and 60 percent fewer fighter squadrons. In 1991, the force had 134 fighter squadrons; today, only 55. The average U.S. Air Force plane is 27 years old.

After 25 years of non-stop deployments to the Middle East, airmen are tired.

“Our retention rates are pretty low. Airmen are tired and burnt out,” said Staff Sgt. Tyler Miller, with the 28th Aircraft Maintenance Squadron based at Ellsworth.

“When I first came in seven years ago, we had six people per aircraft and the lowest man had six or seven years of experience,” he continued. “Today, you have three-man teams and each averages only three years of experience.”

Across-the-board budget cuts known as sequestration that began three years ago forced the Air Force to fire people, meaning those who stayed had to work extra shifts. And instead of flying, pilots are having to do more administrative jobs once taken care of by civilians, who were let go.

"Honestly, from the perspective of an air crew member, the squadron is wiped out," said Jarding.

Then there is the shortage of parts, which is pushing the Air Force to get creative in order to keep these planes airborne. They have had to cannibalize out-of-service planes from what is known as "The Boneyard," a graveyard in the Arizona desert for jets that are no longer flying.

They strip old planes of parts, but now there aren't many left -- posing an obvious problem.

Like their counterparts in the Marine Corps, they even cannibalize museum aircraft to find the parts they need to get planes back into combat.

Capt. Travis Lytton, who works to keep his squadron of B-1’s airborne, showed Fox News a museum aircraft where his maintainers stripped a part in order to make sure one of his B-1s could steer properly on the ground.

“We also pulled it off of six other museum jets throughout the U.S.,” Lytton said.

On the heels of the Fox News reports on budget cuts impacting Marine Corps aviation, Pentagon Press Secretary Peter Cook was asked last week if Defense Secretary Ash Carter thought the problems were more widespread.

“No, I do not think so,” Cook replied. “I think this is a particular issue that's been discussed at length and this is an issue we're working to address.”

But the airmen’s concerns suggest the problem is broader than the Pentagon would like to admit.

Similar issues can be witnessed for the 20th Fighter Wing at Shaw Air Force base in South Carolina, home to three squadrons of F-16 fighter jets.

Out of 79 F-16’s based at Shaw, only 42 percent can actually deploy right now, according to the commander of the wing, Col. Stephen F. Jost.

That's because they, too, are missing parts. One F-16 squadron that recently returned last month from a deployment to the Middle East had a host of maintenance issues.

“Our first aircraft downrange this deployment, we were short 41 parts,” Chief Master Sgt. Jamie Jordan said. To get the parts, the airmen had to take parts from another jet that deployed, leaving one less F-16 to fight ISIS. At one point, Jordan said they were taking parts from three separate aircraft.

When asked about the efficiency of taking parts from expensive fighter jets, Jordan said the costs were not just in dollars: “From a man-hour perspective, it's very labor intensive and it really takes a toll.”

The airmen’s concerns boil down to more than just the hassle on the airstrip: It’s whether the U.S., which for decades has dominated the skies, would be ready for a conventional war with another major world power. Jost warned if one broke out soon, the U.S. would “take losses.”

Said Boswell: “The gap is closing and that worries all of us.”