The U.S. Air Force, by far the largest presumed user of the F-35 fighter, has agreed to declare initial operational capability with a much more limited software and weapons capability that initially planned, according to a report sent to Congress May 31.

The Air Force now plans to declare initial operational capability (IOC) with 12 F-35As (and trained pilots and maintainers) in December 2016, before the long-awaited 3F software package is fully tested. The service previously planned to wait for the 3F package because it allows for an expanded engagement envelope and more diverse weapons.

The 3F release adds capabilities that are key to the F-35’s core mission‚ such as multi-ship suppression, destruction of enemy air defenses and new air-to-air and air-to-ground modes. This package also will include the full complement of weapons carried internally and externally on the aircraft. It is slated for inclusion on the LRIP 9 aircraft, and is expected for delivery at the end of the development program in 2017.

“This [plan] is capability based” and the 3I software satisfies the service’s initial needs, says an Air Force spokeswoman. “We still believe we need 3F for full mission capability.”

In testimony to Congress this spring, F-35 Program Executive Officer Air Force Lt. Gen. Christopher Bogdan said there is “moderate” risk in prime contractor Lockheed Martin delivering the 2B/3I package in 2015, while he acknowledged more risk in meeting the 3F schedule two years later.

“The F-35 is a vital capability that the nation needs to stay ahead of adversary technological gains, and it provides the multi-role capabilities that the anti-access and area denial environment of the future will require,” said USAF Gen. Mark Welsh, Air Force chief of staff.

The Air Force plans to buy 1,763 F-35As; the A-model is expected to be the largest international seller to JSF partners as well as Israel, Japan and, possibly, Singapore.

Meanwhile, the U.S. Marine Corps is planning to declare IOC with 10 F-35Bs, designed for short takeoff and vertical landing (Stovl), as well as trained pilots, maintainers and support equipment, in December 2015. This is a slight shift of the most recent plan to attempt an IOC in summer 2015. The Marines will be the first customer to declare IOC with the aircraft, and they were aggressive in their approach because their aging AV-8Bs are difficult and expensive to maintain. The last Harrier is slated to retire in 2030. “The F-35 is our country’s best hedge against the ever-evolving and unknown threats posted by our adversaries,” says Marine Lt. Gen. Robert Schmidle.

The 2B software will include basic close-air-support and interdiction activities as well as initial air-to-air and data-linking capabilities. Weapons included will be the AIM-120C7, Joint Direct Attack Munition and GBU-12 laser-guided, 500-lb. bomb. The 2B package has been released to the test force.

Italy and the United Kingdom also are planning to purchase the F-35B

The Navy, which has pursued a risk mitigation strategy of buying Boeing F/A-18 E/Fs and EA-18Gs while waiting for the F-35, is taking a more conservative approach toward welcoming the aircraft carrier-capable F-35C into service. The Navy plans to declare IOC in February 2019. The Navy leadership emphasizes in its statement about the IOC plans that it will need the F-35C to “find, fix and assess threats, and, if necessary, track, target and engage them with lethal results in all contested environments.” These capabilities will require, at the least, 3F software as well as training to a larger mission set for an IOC declaration.

By contrast, the Marine Corps and Air Force are taking an incremental approach, allowing for limited use of the aircraft for IOC with a growth path as more capability is delivered to the fleet, eventually culminating in a full operational capability.

Congress directed the Pentagon to declare these IOC plans last year, but allowed for a later release of the information as the Joint Program Office shored up plans for the budget and to assess progress in flight testing.

The services had shied away from declaring IOC owing to numerous past slips in the program; top brass did not want to be seen capitulating on yet another delay. But this now allows for program overseers in the Pentagon and Congress to measure progress against firm plans to introduce the variants into service.

This also allows for the services to craft plans for retiring older aircraft that will be replaced with the F-35, such as the F-16C/D, A-10 and AV-8B.

While establishing a benchmark, the IOC plans also put pressure on Lockheed Martin to make good on its software testing plans. “Our top priority is to continue to execute our plan to support these IOC dates, starting with the Marine Corps in December 2015. Lockheed Martin is committed to cost effectively delivering the F-35’s unprecedented 5th-generation capabilities to the warfighter,” company spokesman Michael Rein said in a statement.