From the outset of its development, Lockheed Martin's F-35 Joint Strike Fighter was designed to have a low-radar cross section, making it difficult to detect by enemy radar. Just like its stealth predecessors, such as the F-117 Stealth Fighter, it incorporates special radar absorbing materials and internally stowed weapons - helping to reduce its signature.
All this means, in theory, the F-35 can operate in airspace where there is a high threat from anti-access/area-denial (A2/AD) weapons such as surface-to-air missiles. Proponents of stealth technology point to legacy platforms such as the F-117 and B-2 bomber as proof of its success. Only one stealth aircraft has ever been shot down in the 30 years they have been flying.
But potential adversaries, such as China, are significantly upgrading their A2/AD capabilities with the development of newer radar systems which can detect stealth aircraft. Stealth secrets have also been stolen through espionage. In 2010, Noshir Gowadia, one of the creators of the B-2 bomber, was convicted of giving classified information to China and other countries.
So not only will countries such as China have upgraded radar systems, they will also know how to nullify any advantage that stealth aircraft have.
Protecting non-stealth aircraft with jamming technology
That's not good news for the US military's older fleet of aircraft. The US Air Force's current 'Teen Series' jets such as the F-15, F-16 and F/A-18 - often designated 4.5-generation aircraft - have very limited stealth characteristics. External fuel tanks and weapons and a lack of radar-absorbing materials means they are highly visible on radar and, thus, vulnerable in A2/AD environments.
If these 4.5-generation aircraft operate in a contested environment where A2/AD weapons are deployed, they will often be supported by aircraft with electronic jamming capabilities. To protect its fleet of F/A-18 aircraft during missions, the US Navy uses Boeing's EA-18G Growler electronic warfare (EW) aircraft kitted out with advanced radar jamming equipment.
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The F-35 is fitted with its own EW capabilities in the form of Northrop Grumman's AN/APG-81 active electronically scanned array (AESA) radar system. Advocates of the F-35 programme say a separate jamming aircraft is not needed because of this technology. It can emit frequencies which can confuse and disable Russian anti-aircraft systems such as the advanced S-400, which uses radar to lock onto enemy aircraft.
There are, however, some figures in the US Navy and industry which say the F-35's stealth and EW capabilities are simply not enough.
After a House Armed Services air and land force subcommittee hearing in March, Rear Admiral Michael Manazir, the US Navy's director of air warfare, told reporters that the Growler emits more jamming frequencies than the F-35, making it a much more capable EW platform.
A more realistic operational scenario, he said, would be for the Growler to support F-35 missions in a complementary role.
It is an admission that the US Navy is not entirely comfortable with the F-35's capabilities in A2/AD environments. So much so that in March it was revealed the US Navy included another 22 EA-18G Growlers on its unfunded priorities list for the 2015 fiscal year budget, costing $2.14bn. Chief of Naval Operations Admiral Jonathan Greenert said he saw a growing need for the Growler aircraft.
A 'questionable' capability - cancelling the F-35
For some commentators, the purchase of more Growlers is seen as the US Navy's "escape hatch" from the unpopular F-35 programme - which has historically received a lukewarm reception from some sections of the service.
And it's not just in the US Navy where people worry about the F-35's performance in penetrating advanced air defences. In a May 2014 article for Air & Space Power Journal, a senior USAF officer questioned the F-35's capabilities and said there were still good reasons to cancel the programme.
"Even if funding were unlimited," Colonel Michael W. Pietrucha wrote, "reasons still exist for terminating the F-35."
The former EW instructor added: "Our assumptions about the operational environment, made more than a decade ago, do not match the current reality...The mission of the aircraft - to penetrate the most advanced air defences and drop precision-guided munitions on critical targets of a peer adversary - remains questionable at best."
An alternative, according to Pietrucha, would be to terminate the air force's participation in the F-35 programme. Instead, the USAF would maintain a limited amount of F-35As - as a replacement for the retired F-117s - and upgrade older fourth-generation airframes with fifth-generation technology.
Like the US Navy with its Growler aircraft, Pietrucha says the US Air Force should build up its EW aircraft fleet, which has "dwindled" since the retirement of EF-111G and F-4G aircraft twenty years ago. That seems to fall on deaf ears, however, as the air force is planning to reduce its EW capabilities even further with the mothballing of several EC-130 EW aircraft.
Boeing campaigns to restore funding for Growler
Pietrucha's article couldn't come at a better time for Lockheed Martin's rival Boeing. It's no secret that, behind the scenes, Boeing has been actively lobbying defence officials in order to keep the F/A-18 production line open past 2016. An order for 50 to 100 more Growlers would do just that.
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But Boeing has to walk a careful line in its campaign to restore funding for its Growler aircraft, said Amy Butler, senior Pentagon editor at Aviation Week.
"The company has to make the case that without more Growlers, even the stealthiest aircraft in the Pentagon's fleet are vulnerable to emerging air defences," she said. "This is a thorny and challenging argument to make as it quickly veers into classified territory."
"And its Pentagon customer is loath to acknowledge that its multibillion-dollar investment in stealth aircraft could be made vulnerable by comparatively small investment in networked air defences," she added.
At its current production rate, Boeing's Super Hornet and Growler production line in St Louis, Missouri, will stop in the third quarter of 2016. According to Boeing, the programme supports 60,000 jobs in the US and accounts for $3bn in annual economic impact.
In May, Boeing celebrated delivering the 100th Growler to the US Navy, a major milestone for the programme. In what may be an allusion to the F-35's ongoing costs increases and delays, Captain Frank Morley, US Navy F/A-18 and EA-18G programme manager, said the Growler programme was "all on cost and on schedule".
"We believe there is a compelling case to be made that the navy needs 50 to 100 more aircraft to meet future requirements," he added.
Investing in more EW aircraft - between a rock and a hard place
Pentagon officials are in an awkward position. If the Pentagon was to invest in more EW aircraft - such as the Growler - it would signal a lack of faith in the F-35's capability to penetrate enemy airspace. Equally, if it didn't invest in additional EW capabilities, the lives of F-35 pilots could be at risk with the proliferation of more advanced A2/AD weapons in countries such as China.
The grounding of the entire F-35 fleet at the beginning of July, after an engine fire on an air force F-35A, will only add to concerns. Technical risk is still a significant factor in the F-35 programme and while its ability to fly in contested environments is not likely to affect the delivery schedule, it is a problem which questions the F-35's fundamental role as a fifth-generation stealth fighter.