The Ministry of Defence has declined to provide a completion timeline for the F-35 Block 4 upgrade programme, telling Parliament it does not routinely comment on detailed delivery schedules.
The written answer, given by Minister for Defence Readiness and Industry Luke Pollard on 21 May in response to a question from Ben Obese-Jecty MP for Huntingdon, stated that the Block 4 programme continues and did not impact the declaration of Lightning Full Operating Capability. Pollard said the upgrade “will further develop our world leading Combat Air capability, the UK Lightning, through improvements in lethality, survivability and supportability.”
Block 4 is the designation given to the current major software and hardware upgrade standard for the F-35 across all variants. It introduces new weapons integration, enhanced electronic warfare capabilities, improved sensor fusion, and expanded connectivity.
The Block 4 upgrade has experienced significant delays and cost growth that affect all F-35 operator nations, including the UK. The upgrade was originally intended to deliver 66 new capabilities by 2026, but that deadline slipped first to 2029 and then further still, with the US Government Accountability Office assessing in September 2025 that even a reduced scope of capabilities would not be complete until at least 2031, representing a five-year slip from the original timeline.
The root cause has been the Technology Refresh 3 hardware and software package, a $1.9 billion upgrade that provides the enhanced processing power Block 4 requires. TR-3 suffered persistent hardware immaturity and software instability issues, leading to a year-long halt on F-35 deliveries in 2023 while Lockheed Martin stored completed jets at its Fort Worth facility. All 110 F-35s delivered in 2024 were late by an average of 238 days. Block 4 costs have grown from an original estimate of $10.6 billion to at least $16.5 billion as of 2021, with a further $6 billion in overruns identified since.
The Pentagon has narrowed the programme’s scope to focus on capabilities achievable by 2031 without requiring an engine upgrade. For the UK, the delays are directly relevant to the broader question of when the Lightning Force will achieve the full weapons capability envelope originally planned for the aircraft.
The programme has faced delays across the global fleet, according to a letter from MoD Permanent Secretary Jeremy Pocklington to the Public Accounts Committee, published earlier this month, acknowledged that the Global Spares Pool has struggled to keep pace with the delivery of new F-35 aircraft into the worldwide fleet and that the F-35 Joint Programme Office has launched a Global Sustainment Solution Reset project to address this.
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Does block 4 as originally envisaged still exist? Are we not going to see small upgrades done, year on year, with new processors, new radars (are we still allowed to call them radars?) made available when they are ready, engine upgrades happening less frequently, software more frequently, and always, always needing regular upgrades, just like any technology?
If what we are wanting to know is when can we get Meteor on there, that’s what we need to ask. If the question is when do we start to upgrade and how that’s what we should ask, and if the question is when will it be safe to buy something that won’t change and we can take a breath, the answer is never. Deal with it!
Cross our fingers Meteor is included in this “by 2031” group of upgrades I guess.
AIM-260 has absolute priority over Meteor – once thats integrated and selling like hotcakes, they might integrate Meteor
Tbh, F35 delivered since 2023 have 0 combat capabilities. Not some, like TR2. TR3 have 0 combat capabilities. So integration of meteor… well… TR2 are not mission capable for naval strikes right now. TR3 are not capable of anything else than flying, according to GAO office and many other US official statements.
This explains why a country like Belgium which received it’s planes in 2025 refuses to send it’s F16 a/b MLU to Ukraine, dispite previous engagement.
I am not talking about the availability rate of the plane, I just mention the 400 planes that have been delivered and that cannot shout a Sidewinder.
TR4 calendar has switched from 2026 to 2031 and the scope of TR4 is shrinking every year. The new reactor is delayed and the new auxiliary power unit to cool down equipment are not ordered, since they are far from being developped. So the rest of TR4 may arrive in 2038, at best. Meaning that the programme initiated in 1993 will work (simply work as specified) 42 years after program started. At the moment, F35 A is inferior to Typhoon bloc 3 and much more to Typhoon Quadriga, not even talking about Rafale F3R, nor F4. When the Rafale F5 will be ready, we won’t even need to use passive sensor, the radar will be sufficient, for the semi fleet in the air.
UK is wise to let the F35 mature and not to buy any more planes. And the TR2 will never accommodate new weapons. USA not being able to stabilize evolution of the code 4 years in a row is about to abandon the TR2 évolution to concentrate all available means on TR3. Because TR3 is for planes just able to fly at the moment, and this is true for the third year in a row, with 400 incapables planes. Reports are on the web, anyone can read them. And aim 260/meteor debate does not exists at all. Right now, the debate is aim9 and gun or nothing.
And given the numbers of F35 delivered to European armies, it is not a good sign.
twice as expensive and no firm deadline for availability.
sounds a lot like the Swiss deal.
the gift that keeps on giving.
2038 is the most realistic. Delays in F35 takes at least 6 months every year.
Oh did we buy some thing that cost way more than we were told it will, with delays in to service and expensive up grades, again. Well done the MOD money well spent on an aircraft that has ditch fuel or weapons as can not land with a full load, And has a shorter range than over variants,
No carrier aircraft can land with a full fuel or weapon load.
Mitsubishi Zero? Maybe a different context though. And maybe a different meaning of land.
F35 may be able to take off with weapons, but TR3 have no capabilities, at all, to use them.
Or to put it another way they haven’t got a clue. ‘🤔
nor can civil aircraft but the variand we have can not land verticaly when heavy, stunning idea for a choice of aircraft,
Utter bollox. UK can vertically kand with their heaviest weapons loadout. No weapons have ever been ditched because of inability to land.
so i have been imformed wrong, thats ok i do not mind being corrected,
Since they are TR2, yes. But no stable software releases 4 years in a row now. So forget about weapons upgrades.
In shock news MoD can’t give a timeline for something they have no control over
Yeah it’s not like the UK government put all its eggs in one basket when buying the aircraft is it- and we have no sway whatsoever. Personally, all things considered I think the whole UK F35B procurement saga has been disappointing. I’d love to think Tempest could.produce something more home grown for the carriers but accept we will be lucky if we get anything at all out of that ‘project’ at all TBH.
I have to agree, we started out as a tier 1 partner, but somehow dont have access to the source code?
Just how the hell was this allowed to happen?
That aside, the immense complexity of the F35B has always been a concern, especially compounded with the UK MOD’s typical maintenance and support on a shoe string model that means as the fleet reaches its full initial quota and a fleet that now be really getting into its stride, we actually find out its heading the opposite direction!
With only a handful of combat capable airframes available at at any one time, aircrew flight hours falling, still a lack of maintenance personnel etc, etc.
A fleet of 47 airframes and an ability to raise 12 combat capable aircraft at a push, is pathetic quite frankly.
We would need a pool of 200 to raise 4 operational squadrons at this rate!!
Im afraid I’ve come to the conclusion we should be looking to replace the fleet in tbe 2040’s, with a new, far simpler carrier capable fighter.
While availability of the A model will no doubt improve with updates, I think the B is a development dead end, its ‘massively’ over complicated and I doubt reliability and mission availability rates will ever be terribly good.
In the future, the RN are going to have to get 36 on a QE deck, on a wartime footing, just to try and have 24 operational!
Its certainly no secret that LM can’t wait to drop the B and C model and simply concentrate on future advanced A models to compliment the F47 in service.
Lockheed is the design authority. The UK could do what Israel does and have a separate overlay but that means that UK integrated weapons will not work with all other F35s. Interoperability and larger potential markets means its in the UK’s intrest to retain common software. A separate overlay would also mean the UK would have to pay the cost of air safety qualification and assume all risks. That’s significant cost and a much higher risk profile.
A higher risk profile than having none of the UK weapon systems integrated until the 2030s Ron, thats ‘very’ debatable…
I can only hope lessons have been well learnt.
You think starting from scratch will magically make safety critical software come into service quicker. I have a surprise for you.
Well yes it will Ron, the UK requirements are ‘well’ down the F35 list, one obvious reason is that the US MIC want US weapon systems F35 integrated and in the show room first, they certainly don’t want foreign competitors available and chipping away at their bottom line profits.
After the frankly piss poor experience of F35, I doubt we will ever buy US fast jets again…
You have no idea what you are talking about. There are finite number of people that have SC clearance and know how to write software that carries mitigation for risks out to 12 million to one. Guess what they are already working on something else.
Does anyone know how much effort/money the UK MoD is putting into Meteor/Spear3 integration for F-35? I note that JSM integration seems to be coming along nicely & that is a non American weapon. Perhaps Norway is funding it properly? I also see that Israel is about to start production of drop tanks for its F-35
Don’t worry, USA have no control either on whats happening in this program. Neither the JPO, Lockeed or US army have any control on this program. UK is one of 13 air forces in Europe that have disappointements with this system.
Well that makes it sooooooo much palatable then.
A timeline for block 4 is based on LM promises, good luck with that. Block 4 will be degraded due to the F135 ECU not being ready anytime soon in significant numbers. A shame the AETP engine program for the F-35A (maybe C as well) was terminated. This would not help B users though.
Its a shame the Anglo American F136 engine didn’t proceed.
Yes, TR4 delivery has sleeped from 2026 (in 2019) to 2031 (in 2026), extremely optimistic and most likely 2037, by the looks of it.