At Marine Corps Air Station Beaufort in South Carolina, both British and American pilots are learning how to fly the F-35B. (Jeff Martin/Staff) Jeff Martin

The Pentagon announced Thursday it is grounding its entire fleet of F-35s, just days after the first crash of an F-35B led investigators to suspect there is a widespread problem with the advanced fighter’s fuel tubes.

“The U.S. Services and international partners have temporarily suspended F-35 flight operations while the enterprise conducts a fleet-wide inspection of a fuel tube within the engine on all F-35 aircraft,” the F-35 Joint Program Office announced in a statement Thursday morning.

“If suspect fuel tubes are installed, the part will be removed and replaced. If known good fuel tubes are already installed, then those aircraft will be returned to flight status. Inspections are expected to be completed within the next 24 to 48 hours.”

The office said the grounding “is driven from initial data from the ongoing investigation of the F-35B that crashed in the vicinity of Beaufort, South Carolina on 28 September. The aircraft mishap board is continuing its work and the U.S. Marine Corps will provide additional information when it becomes available.”

In the Sept. 28 crash in South Carolina near the Marine Corps Air Station Beaufort, the pilot safely ejected from the aircraft, which belonged to 2nd Marine Aircraft Wing, Marine Fighter Attack Training Squadron 501, known as the “Warlords.”

While the F-35′s U.S-based Joint Program Office had indicated that the grounding included aircraft purchased by foreign militaries, the British military signaled Monday that its entire fleet is not grounded.

The F-35 Joint Program Office has said safety is a top priority.

“The primary goal following any mishap is the prevention of future incidents. We will take every measure to ensure safe operations while we deliver, sustain and modernize the F-35 for the warfighter and our defense partners.”

The U.S. grounding comes after the Pentagon announced that a Marine Corps F-35B conducted the platform’s first-ever combat mission on Sept. 27. The Marine Corps' aircraft launched from the amphibious warship Essex, striking targets in Afghanistan.

In April, a Marine Corps F-35B out the Marine Corps air station at Cherry Point, North Carolina, was forced to make an emergency landing when the aircraft fuel light came on.

The grounding news also comes two days after Defense News reported that Secretary of Defense Jim Mattis has ordered the military services to get readiness rates on four planes, including the F-35, up above 80 percent by next September.

According to data for fiscal year 2017, the most recent available, the Air Force’s F-35A models had around a 55 percent readiness rate, well below that target.

Although the Marine Corps is the first U.S. service to fly its joint strike fighters in combat, the aircraft has been used by the Israeli air force to strike targets. In May, Israel Defense Forces officials confirmed that the country’s F-35 “Adir” fighters had seen combat in two airstrikes somewhere in the Middle East.

The Marine Corps declared the F-35B operational in 2015, becoming the first service to integrate the joint strike fighter into its fleet. The Air Force followed by declaring initial operational capability for the F-35A conventional variant in 2016, while the Navy plans to declare initial operational capability for the F-35C carrier variant in February 2019.

The F-35 joint strike fighter is the most expensive program in the Pentagon’s history.

Currently, the U.S. military has purchased 245 aircraft from Lockheed Martin. The Air Force has 156, the Marine Corps has 61 and the Navy has 28, according to data provided by the joint program office.

The U.S. Air Force, Navy and Marine Corps plan to buy a total of 2,456 F-35s, at an estimated cost of $325 billion. In total, the aircraft program is projected to cost about $1 trillion to develop, produce, field and sustain over its lifetime, according to the Government Accountability Office.

The F-35B is the short takeoff, vertical landing variant of the aircraft, which allows the pilot to hover and land vertically like a helicopter — a necessity for the Marines, which typically operate from amphibious ships with smaller decks than aircraft carriers.

Because the problem is related to a fleetwide engine issue, rather than just in the F-35B models, it appears unlikely that the problem is unrelated to the short-takeoff and vertical-landing capabilities of the Marine’s design.

The issue as described by the JPO indicates the issue is believed to come from a subcontractor who supplied the fuel tubes for engine manufacturer Pratt & Whitney.

A spokesman for the F-35s manufacturer, Lockheed Martin, said Thursday morning that industry partners were working with the F-35's Joint Program Office to investigate the problems.

"We are actively partnering with the Pentagon’s F-35 Joint Program Office, our global customers and Pratt & Whitney to support the resolution of this issue and limit disruption to the fleet,” said Friedman, Michael, the spokesman for Lockheed.

The U.S. Government Accountability Office has projected a total lifetime cost of $1 trillion for the program. F-35s have already been delivered to the United Kingdom, Italy, Israel, Netherlands, Turkey, Australia, Japan, South Korea and Norway.

This story is developing and will be updated.

Defense News staff writers Aaron Mehta and Valerie Insinna contributed to this report.