The Marine Corps will soon conduct an operational readiness inspection (ORI) of its first squadron of F-35Bs, the final step before declaring that the jets are finally combat ready.

Marine Fighter Attack Squadron (VMFA) 121, based in Yuma, Ariz., will be the first unit to declare initial operational capability of the jet sometime between now and December. The ORI will basically see the squadron complete a checklist of operational capabilities including sortie rates and maintenance turnaround time, said Joe DellaVedova, a spokesman for the Pentagon’s F-35 Joint Program Office (JPO).

After the ORI is complete, the commander of VMFA 121 will submit the results to Deputy Commandant for Aviation Lt. Gen. Jon Davis, who will then declare IOC if he is satisfied the unit has enough trained pilots, spare parts and maintenance infrastructure in place.

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The last batch of four F-35Bs were delivered this week in preparation for the OIR, which is scheduled to begin the second week of July, according to the Marine Corps.

The squadron will have at least 10 aircraft before declaring IOC, of which nine are currently on the flight line at Yuma, DellaVedova said. The aircraft are outfitted with the 2B version of the F-35’s operating software, which has limited capability to deploy weapons but is scheduled to be upgraded to the final 3F software once manufacturer Lockheed Martin finishes its validation.

VMFA 121 also has the most up-to-date version of the autonomic logistics information system (ALIS), which automatically downloads maintenance data from the aircraft after each flight, diagnoses any functional issues and prescribes a fix.

A declaration of IOC has been more than 14 years in the making and is a major milestone for a program that has suffered cost overruns, developmental delays and has gained renown as the most expensive weapons system in the world.

Since a re-baselining of the $400 billion F-35 program in 2010, both the JPO and Lockheed Martin [LMT] have generally stuck to self-prescribed deadlines. The Air Force F-35A is scheduled to become operational in 2016, followed by the Navy F-35C in 2018.

The Marine Corps recently completed a series of operational tests with six F-35Bs aboard the amphibious assault ship USS Wasp (LHD-1) in the Atlantic Ocean. From May 18-29, the aircraft performed 108 sorties. Each pilot also carried out four take-offs and landings at night without the assistance of either night vision goggles or the jets’ distributed aperture system, according to the JPO.

Lockheed Martin is now in a dead sprint to bring the per-aircraft cost of an F-35A, without the Pratt & Whitney [UTX] F135 engine, in line with fourth-generation fighters by 2019. The company is aiming for each jet to cost less than $80 million by that time, down from a current price of over $100 million. A ramp up of production at the company’s Fort Worth, Texas, manufacturing facility in preparation for deliveries to international customers is expected to help achieve an economy of scale.

The U.K. Royal Air Force (RAF) also will fly the F-35B and its pilots already are training with the jets. A British pilot in June executed the first “ski-jump” launch at Naval Air Station Patuxent River in Maryland. Initial testing of the aircraft launch maneuvers were aimed at demonstrating the jet’s ability to take off and land from the British-style aircraft carrier ramp.

“Ski-jump ramps provide the aircraft with an upward flight path meaning the aircraft can take off from the available distance with a greater payload, which means more weapons,” according to Lockheed Martin.

The F-35 has come under fire particularly because the Marines will declare IOC without its full offensive capability. Weapon separation testing is ongoing, but the 2B software loaded on the Marine Corps jets does not allow for an array of weapons the aircraft eventually should be able to carry. Neither the F-35B or F-35C have a gun, though the Air Force’s F-35A does have a 30mm cannon embedded in a bubble inboard of the left wing. Both the B- and C-models will eventually have the option of carrying a gun pod mounted to the belly of the aircraft.

On June 12, an RAF pilot successfully released toe inert 500-pound Paveway IV precision-guided bombs, the first dual-mode bomb release for the aircraft.