The U.S. Marine Corps on Tuesday established its first operational squadron of F-35 fighter jets at an air station in Yuma, Arizona, a move that officials said showed progress on the Pentagon’s biggest and most scrutinized weapons program.

Three F-35B fighters built by Lockheed Martin Corp have already arrived at the base, with 13 more to come over the next year. The service has also spent about half a billion dollars to build new hangars for the planes, a high-end flight simulator for training pilots, and maintenance facilities, according to Captain Staci Reidinger, a spokeswoman for the base.

The new squadron, which is slated to start initial flights later this year or early next, was formally unveiled at a ceremony at the Arizona air base that included top Pentagon and Lockheed executives, as well as Senator John McCain of Arizona, the top Republican on the Senate Armed Services Committee.

It marked good news for the radar-evading Lockheed fighter program, which has been restructured three times in recent years to save money and allow more time to work out technical kinks.

Marine Corps Commandant General James Amos said it was a historic day for the smallest of the U.S. military services, which urgently needs to replace its aging fleet of older model F/A-18 fighters built by Boeing Co, and AV-8B Harrier jets, which are growing expensive to maintain.

“This squadron will be the first, not only in the Marine Corps or the United States, but the first in the world to bring a fifth-generation, multi-role, (short takeoff vertical landing) stealth fighter ... into an operational status,” he said in a speech at the base. A copy of the speech was made available to Reuters.

Amos, who flew the F-4 Phantom fighters that were used extensively during the Vietnam war, said the new plane had “eye-watering” capabilities, although he said he could not discuss most of them since they are classified.

He said establishment of the squadron at the Yuma air base, coupled with testing and training going on elsewhere, showed “tangible progress” on the F-35B model, which can take off from shorter runways and land vertically like a Harrier jump jet.

Just two years ago, the Pentagon had threatened to cancel the F-35B program unless it made significant technical progress.