Top U.S. Marine Corps officials hailed progress on the next-generation F-35B fighter jet built by Lockheed Martin and said military training flights could be approved by late March or early April.

Assistant Marine Corps Commandant General Joseph Dunford said there was clearly “irreversible momentum” on the Marine Corps version of the new fighter jet, which came out from under the threat of cancellation in January, when the Pentagon took it off “probation” a year ahead of schedule.

“We really feel pretty good about where we are today,” Dunford said in an interview on Friday after a ceremony marking the arrival of three F-35B jets at Eglin Air Force Base in northwestern Florida, where Air Force, Navy and Marine Corps pilots and mechanics will be trained on the stealthy jets.

Eglin is home to the largest fleet of F-35s anywhere at the moment: six conventional takeoff and landing F-35A models, built for the Air Force, and three F-35B models, which can take off from shorter runways and hover and land like a helicopter.

“You can just sense when success starts to feed success, and it’s the snowball that starts to roll, and I really believe that’s where we are today,” Dunford said.

Lockheed Chief Executive Robert Stevens and other top Lockheed executives also flew in to attend the ceremony, which was held in one of two cavernous, brand new hangars built at the air base to house the Navy and Marine Corps jets.

Stevens, a former Marine, said the start of training would be another step forward for the Pentagon’s biggest weapons program, a “hugely ambitious” project to replace over a dozen fighter planes in use all over the world with three variants of a single airplane design.

“We’re getting closer to the initial operational capability and the deployment of that jet,” Steven told Reuters after addressing over 200 people at the hangar ceremony. “Every pilot says, ‘Give me this airplane.’ They’re anxious to get started.”

Dunford said the F-35B brought together stealth, supersonic speed, vertical landing and other capabilities never before seen in a single plane. “The F-35B is more than just a new fighter. By replacing so many different capabilities in our arsenal it represents a new way of doing business,” he said in his speech.

Defense Secretary Leon Panetta defended his decision to lift the F-35B probation in a letter to the leaders of the Senate Armed Services Committee, who argued the move was “premature.” Panetta said he was “acutely aware of the many challenges” still facing the F-35 program, and continued to monitor it closely.

Dunford’s endorsement of the jet comes as the Pentagon is restructuring the program for the third time in recent years, postponing orders for 179 planes to save $15.1 billion over the next five years. Officials insist it still plans to spend $382 billion for a total of 2,443 F-35s over the next decades.

Those plans have prompted Washington’s eight international partners on the multirole fighter to rethink their own orders. Canada has invited officials from the other countries—Britain, Australia, Norway, Denmark, the Netherlands, Italy and Turkey—to meet in Washington next week to get an update on the program.

Wing Commander David Arthurton of Britain’s Royal Air Force said the F-35 was “a work in progress” and adjustments to partner orders reflected their own budgetary pressures. “It’s a reality of doing business in this day and age,” he told Reuters.

Stevens said Lockheed remained committed to improving its performance on the weapons program, which will account for about 20 percent of company revenues when it hits full production.

The program has seen cost increases and schedule delays typical of big arms development projects, but the cost of developing a separate new airplane for each of the dozen the F-35 will replace would be far, far higher, Stevens said.

“I’m accountable for the execution on this program. We’re going to do a better job,” he said, adding that issues common to most new aircraft programs sometimes overshadowed the steady progress being made on the F-35. “We’ve had some setbacks … and we’ve had some huge successes,” he said.

The Pentagon this week said Lockheed forfeited $31.5 million in award fees for work on development of F-35 fighter jets in 2011, the second consecutive year it did not meet some pass-fail Pentagon development goals for the aircraft.

Lockheed this week said current plans called for 1,001 test flights in 2012 to accomplish over 7,800 test points, but that number could expand throughout the year. It said 114 flight tests had been this year to date, hitting 773 test points.

The Air Force is expected to issue a military flight release for the new radar-evading supersonic F-35A jets within weeks, followed by approval for flights of the F-35B jets in early spring, said Colonel Arthur Tomassetti, vice commander of the 33rd Fighter Wing at the base, which is responsible for training U.S. military forces to operate the new planes.

Tomassetti, a military test pilot who has been involved with the F-35 program since its start, said there were over 1,000 people in the fighter wing, including 40 pilots from all three services, each of whom had over 1,000 flight hours.

Flight training was starting later than initially planned, but would ramp up steadily over this year, he said. Pilots and maintainers were already using simulators to learn as much about the airplane as they could. Some had also traveled to other F-35 bases to observe maintenance procedures there, he said.

“We have not wasted the extra time we’ve been given,” Tomassetti told Reuters.