The US Marine Corps says its first combat F-35 squadron is “ready for battle,” but after 14 years of development marked by cost increases and delays, it is time for the combat jet to prove it is as advanced, stealthy and lethal as advertised.

The fifth-generation fighter, conceived in the mid-1990s, has travelled a long, long road to reach initial operational capability, arriving five years behind the original target.

No doubt, the 31 July decision is a historical step forward for the programme, and the industry team has every reason to celebrate, but the road ahead is difficult and there will be scrutiny at every turn.

Ten nations, not counting Denmark and Canada, are counting on Lockheed to deliver more 3,000 combat aircraft to replace rapidly aging fighter forces.

With two years and just under 40% of operational testing remaining, there are plenty of opportunities for new bugs to crawl out of the system.

There have already been several fleet groundings, most recently in June 2014, and dozens of design tweaks, but programme officials says the there are fewer and fewer new problems surfacing. Additionally, the programme claims to have met every target set in the 2010 and 2012 rebaselinings. In fact, the service's IOC announcement on the last day of July means it achieved the objective IOC target set in 2013.

“The weapons system is now in the warfighters' hands and can be called upon to do its mission,” F-35 programme executive officer Lt Gen Christopher Bogdan said in a statement accompanying the announcement. “[We] have worked through a number of challenges as we focused on delivering a stealth fighter that could fly faster than the speed of sound, carry its weapons internally, conduct short takeoffs and vertical landings, and be deployed from amphibious ships and austere bases. We’ve done it.”

F-35B IOC. Lockheed Martin

Lockheed Martin

With the Marines now past IOC, all eyes are now on Hill AFB in Utah where the US Air Force “Rude Rams” fighter squadron is preparing to induct the F-35.

The base expects to receive its first aircraft in September, and one per month after that until a scheduled IOC in August 2016. The air force says it will reach the target despite a maintainer shortfall, but thinks IOC is just a quick pit-stop on its way to full operational capability around 2019.

The first operational navy squadron will declare IOC with 10 carrier-based F-35Cs in August 2018, and the program is also looking abroad, with the UK, Israel, Netherlands and Australia all preparing to stand up their first F-35 combat squadrons at home.

The aircraft has not yet made its international debut, owing to an engine fire last year that grounded the fleet just as the Marine Corps was preparing to fly F-35Bs to the Farnborough Air Show. That debut will instead come later this year when the first Italian aircraft assembled in Cameri, Italy makes its first flight.

Lockheed F-35 programme chief Lorraine Martin said at the Paris Air Show this year that 50% of the aircraft being built over the next five years are for international customers.

Japan’s first F-35 is in assembly at Fort Worth, Texas, and will be delivered next August. The first Israeli F-35I will be arrive in country next year.

Martin says all of the “chunky” development issues have passed with no major showstoppers or problems that keep her up at night, and now the story should be about sustainment and establishing the tactics, techniques and procedures for employing the aircraft in combat.

But Lockheed and the Pentagon must still convince its customers and the wider public that the F-35 is worth the wait and the $400 billion development price tag.

The F-35 team must also convince Denmark and Canada to stick with the programme, since each is reconsidering its commitment to buy 30 and 65 aircraft respectively. Boeing is circling both nations, offering the ready-to-fight F/A-18E/F Super Hornet. Belgium, Finland and Singapore also have fighter requirements, and if the F-35 doesn’t perform as promised it risks becoming political kryptonite to those nations.

The jet also needs more weapons, fast, since the Marines can only employ AMRAAMs, 2,000lb JDAMs and 500lb Paveway IIs in the Block 2B configuration. The biggest milestone of them all in terms of combat capability is the fleet-wide release of Block 3F by August 2017. That would add the 25mm Gatling gun, Small Diameter Bomb, AIM-9X, AIM-132 ASRAAM, 1,000lb JDAM and Joint Standoff Weapon, making the F-35 a true strike fighter.

F-35B IOC. Lockheed Martin

Lockheed Martin