The Pentagon's F-35 Lightning II programme is under mounting pressure to close a widening gap between fleet size and sustainment capacity, a senior US defence official told lawmakers on Wednesday, 24 June. With over 1,300 operational F-35s now deployed across the United States and allied nations, the programme's support infrastructure was designed for roughly half that number.

The Readiness Gap in Plain Numbers

Lieutenant General Gregory Masiello, Programme Executive Officer of the F-35 Joint Programme Office, told the Senate Armed Services Airland Subcommittee that the scale of the problem is structural. 'There are over 1,300 operational F-35s out there, 832 of which are inside the US inventory, and the other ones are with our partner nations,' Masiello said. 'If I have over 1,300 operational aircraft out there, I believe we have set and enabled a sustainment system for about 7 to 800. So there is our challenge in readiness.'

That shortfall — a sustainment architecture built for fewer than 800 jets now supporting more than 1,300 — represents the central challenge before the programme as it enters its next phase of expansion.

How the Programme Has Scaled Since 2016

Masiello placed the readiness challenge in historical context, noting that when the last F-35 programme chief appeared before the Senate in 2016, there were just 170 aircraft in service across 12 participating nations. Today, the programme spans 20 nations, has logged more than 1.2 million flight hours, and has trained over 3,400 pilots.

The aircraft now operates from 42 sites worldwide and 13 ships, including platforms operated by allied nations. The Netherlands and Australia have both declared full operational capability, and several other partner countries have completed delivery of their planned fleets.

Block 4 Upgrades and the FY2027 Budget

The hearing also examined progress on the Block 4 modernisation programme, which is designed to sharpen the aircraft's combat edge against advanced air defences and next-generation threats. Subcommittee Chairman Senator Kevin Cramer described the F-35 as 'a strategic asset that strengthens deterrence, enhances interoperability, and reinforces the alliances and partnerships that underpin global security,' adding that Block 4 upgrades were essential to keeping the aircraft relevant.

Masiello warned that the proposed fiscal year 2027 budget — which includes funding for 85 US aircraft, Block 4 upgrades, and engine modernisation — was critical. 'If we did not get the totality of the budget or only got one portion of it, there's a significant impact on the production line and the number of aircraft,' he said.

Lawmakers Demand Accountability on Costs

Senator Mark Kelly, a former naval aviator and astronaut, acknowledged the aircraft's capabilities but pressed for greater fiscal discipline. 'We need accountability, and we need to have a clear understanding of how the department is improving readiness, controlling costs, and ensuring that the programme delivers on the promises,' Kelly said.

His concerns reflect a broader pattern of congressional scrutiny. The F-35, developed by Lockheed Martin, is the largest and most expensive weapons programme in US history, operated by the US Air Force, Navy, and Marine Corps, as well as allies across Europe, the Indo-Pacific, and the Middle East.

Combat Operations Cited as Proof of Capability

Masiello pointed to recent operations — including missions described as Rough Rider, Absolute Resolve, Midnight Hammer, and Epic Fury — as evidence of the aircraft's unique operational value. 'This is the only aircraft that can hit some of the targets that it was able to hit and see everything that it could be to actually act as a quarterback of that joint force,' he said.

With the fleet set to keep growing, the programme now faces a defining test: whether its sustainment infrastructure can scale as fast as the aircraft itself.