Key Points – The advanced F-35B Lightning II fighters operated by the Royal Air Force and Royal Navy’s Fleet Air Arm will continue to face restrictions in their air-to-ground strike capabilities for the foreseeable future, reports indicate.
-Despite being fifth-generation aircraft, these jets are currently limited to employing Paveway series guided bombs, as the integration of more sophisticated standoff weaponry has been significantly delayed.
-The SPEAR 3 missile program, crucial for enhancing these capabilities, is now not expected to enter service until the early 2030s, a timeline confirmed by the UK Ministry of Defence (MoD).
-This setback means British F-35Bs will operate with a constrained weapons suite, hindering their full multirole potential.
The F-35B Lightning II: A Versatile but Under-Armed Platform
Developed by Lockheed Martin, the F-35B is a cutting-edge combat aircraft renowned for its unique blend of stealth, supersonic speed, and Short Take-Off/Vertical Landing (STOVL) capability. This STOVL function, enabled by a shaft-driven LiftFan propulsion system, allows the F-35B to operate from diverse locations including light aircraft carriers, roadways, and austere forward operating bases. Such versatility reduces logistical demands, increases operational tempo, and facilitates rapid deployment closer to conflict zones.
The aircraft features an adaptable internal weapons bay designed for air-to-ground, air-to-air, or mixed munitions, and can be equipped with a GAU-22A 25mm cannon. For missions where stealth is not paramount, external pylons can boost its payload capacity to over 6,800 kg.
Its advanced sensor suite includes the AN/APG-81 AESA radar, the AN/AAQ-37 Distributed Aperture System (DAS) for threat warning, and the AN/ASQ-239 Barracuda electronic warfare system.
SPEAR 3 Integration Challenges Hinder Precision Strike
Despite the F-35B’s sophisticated design, the integration of the SPEAR 3 missile – a key element for its intended precision long-range strike role – has encountered significant obstacles. Developed by MBDA UK, the SPEAR 3 is a lightweight cruise missile boasting a range exceeding 100 km, guided by a turbojet engine, inertial/GPS navigation, and a data link. Originally slated for service entry in 2025, the missile’s first test firing only occurred in November 2024, launched from a Eurofighter Typhoon. Its certification for the F-35B platform has now been deferred by several years.
Several factors contribute to this delay. A primary issue is Lockheed Martin’s challenges in delivering the TR-3 (Technology Refresh 3) software configuration, a necessary precursor for the F-35’s Block 4 upgrade. This future software iteration is essential for enabling new capabilities, including the integration of the SPEAR 3 missile. Furthermore, stringent U.S. export control regulations and certification processes pose additional hurdles, as Washington’s approval is mandatory for any new weapon integration on the F-35 platform.
Growing Political Pressure for Accelerated Capability
The ongoing delays have sparked considerable criticism within the UK’s political circles. Conservative MP James Cartlidge, a noted defence affairs specialist, has advocated for a more pragmatic and swifter approach to integrating new capabilities, even if it involves accepting a higher degree of risk.
He pointed to Ukraine’s rapid adaptation of its Su-24 aircraft to deploy Storm Shadow missiles as an illustration of how political determination can expedite weapon deployment, even bypassing full certification processes. Cartlidge argues that the Royal Air Force urgently needs modern, integrated weaponry for its fighter fleet to effectively counter evolving threats, particularly from Russia.
UK’s F-35B Fleet Status and Future Plans
According to The Military Balance 2025, the United Kingdom currently possesses 34 F-35B Lightning II aircraft, with approximately 30 actively serving across the Royal Navy and Royal Air Force. These aircraft officially entered service in June 2018 with the 617 Squadron based at RAF Marham, re-establishing Britain’s carrier-capable fighter force following the Harrier’s retirement.
Their inaugural operational deployment was in 2021 as part of Carrier Strike Group 21 (CSG21), heralding the return of UK carrier-based air power. The UK’s initial plan is to expand its F-35B fleet to 48 aircraft, while maintaining a long-term ambition to acquire up to 138 jets, contingent upon industrial capacity and budgetary allocations. The current weapons integration delays, however, cast a shadow on the operational effectiveness of this growing fleet.
