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.
twice as expensive and no firm deadline for availability.
sounds a lot like the Swiss deal.
the gift that keeps on giving.
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.