The U.S. Marine Corps plans to declare initial operational capability (IOC) with the F-35B in late 2015, says Commandant Gen. James Amos.

The Marines are the first customer slated to declare IOC, and as such are willing to use the 2B software package, which allows for a limited flight envelope and limited weapons carriage, in the short term. A more expansive 3F software release is slated for 2017.

The Pentagon plans to report May 31 to Congress on when the Marines, Air Force and Navy will introduce the single-engine, stealthy F-35 into service. This has been an issue of contention as the F-35 program has repeatedly slipped its in-service date due to poor management and execution, along with technical challenges.

Air Force officials have shown a willingness to allow for IOC with the 2B software, but had previously said they would wait for the 3F package, with expanded capabilities, in 2017. The Block 3 software critical design review is slated for this summer, according to April testimony from F-35 Program Executive Officer USAF Lt. Gen. Christopher Bogdan. He also said he has “moderate confidence” that the 2B software will be delivered by prime contractor Lockheed Martin as needed in 2015, with a lower expectation of success in completing the 3F work as needed in 2017.

Critics say the Marine Corps decision to declare IOC — which includes 10 aircraft, 10 fully trained maintenance and flight crews and suitable spares for deployment — assumes too much risk for the service’s ground attack capabilities. However, Capt. Richard Ulsh, a Marine Corps spokesman, says the Marines will continue to operate the AV-8B Harrier, which will be replaced by the F-35B, until 2030.

For IOC, these first 10 aircraft must be “shipboard qualified,” Amos told an audience hosted by the Brookings Institution on May 29. Though this small number of aircraft will be enough for the Marines to accept the F-35B, designed for short takeoff and vertical landing on amphibious ships, the full squadron will consist of 16 aircraft.

Marine Fighter Attack Squadron (VMFA) 121 in Yuma, Ariz., will be the first squadron to become operational. It will be required to deploy to Marine Corps Air Station Iwakuni, Japan, in short order.

The U.K. and Italy are both expected to purchase the F-35B, though their buying plans are not firm.