Greening Defence: RAF Ambitions in Search of Jet Zero

Flying light: the RAF conducts the world's first flight powered by 100% synthetic fuel as part of Project MARTIN in November 2021. Image: Defence Imagery / MOD News Licence

An ambitious strategy promises a net-zero RAF by 2040, 10 years ahead of the rest of Defence. But with no viable carbon-free fuel currently available, the service will need to rely on a close relationship with the commercial aviation industry to achieve a technological breakthrough.

In the interim, a pilot scheme to turn RAF Leeming into a ‘living laboratory’ to experiment with greener infrastructure and energy is proving fruitful and promises much.

With arguably the greatest decarbonisation challenge of all the services, the RAF has also been the most vocal. Aviation emissions account for three-quarters of RAF carbon emissions and half of the Ministry of Defence (MoD)’s footprint, with the Chief of the Air Staff (CAS), Air Chief Marshal Sir Mike Wigston, describing climate change as ‘a transnational challenge, that threatens global existence and our shared security and prosperity’. Although not yet publicly available, an ambitious strategy has been outlined. By 2025, the RAF intends to have created its first net-zero airbase, with the entire estate net zero by 2030. By 2040, the service intends to be carbon net balanced – 10 years ahead of Defence’s scheduled timeframe. Some critics may argue this is overly optimistic, but CAS hopes that this stretch-target will force the RAF to accelerate and move faster. He is under no illusion as to the challenge ahead: ‘it will take decades, it will require collaboration, it needs ambition, and we need to start now’. This ambition might be prudent given the latest UN reporting, but equally runs the risk of betting on technology too early, before the science has been proven. The strategy is divided into three areas: net-zero aviation, estate and Business-as-Usual. As with the other services, there is a clear focus on decarbonisation, providing a useful commonality of language across Defence, encouraging collaboration both internally but also externally with industry, and providing a metric with which to measure progress.

Net-zero Aviation

Just as the Royal Navy faces a challenge resourcing sustainable propulsion, the RAF must discover a carbon-neutral energy source with an output comparable to existing aviation fuel; this is perhaps the single greatest issue across Defence. Unlike the Navy, there are several existing options to start the greening process. Substituting 30% of conventional fuels with Sustainable Aviation Fuel (SAF), or drop-ins, in a jet travelling 1,000 nautical miles reduces CO2 emissions by approximately 18%. While CO2 emissions from global aviation have reduced by 50% since 1990, this has been undermined by the increase in commercial air traffic. In response, the UK government – forced into action by the commercial aviation sector – has formed the Jet Zero Council, headed by the Secretaries of State for Transport and for Business, Energy and Industrial Strategy. This will provide ‘a laser focus on UK production facilities for SAF and the acceleration of the design, manufacture and commercial operation of zero-emission aircraft’. Additionally, the RAF has formed the Global Air Chiefs Climate Change Initiative, providing a forum for 41 national air forces to discuss the issue. This collaboration must be commended; the RAF has avoided the belief that climate change can be mitigated by working in isolation.

Standardising Drop-in Fuels

Part of the problem is standardisation. In November 2020, the Defence Strategic Fuels Authority, working in partnership with industry, made changes to the MoD’s aviation fuel standards to allow for sustainable fuel blends of up to 50%. This allowed thousands of civilian and military aircraft to be fuelled with SAFs in what Defence Secretary Ben Wallace described as ‘simple yet effective steps to reduce the environmental footprint of Defence’. While SAF has been performance tested at 100% in basic military aircraft, incorporating these blends into higher-spec airframes will require adaptation to ensure safety; consequently limits remain in place to gain further data. This is not an issue while SAF production volumes remain low, though longer-term, it is expected that the blend limit will eventually increase to 100%. This measure has wider significance for the global greening of aviation fuels. The Defence standard is used by UK civil and commercial airlines and by many NATO countries to influence their choice of fuel; this is one area where the RAF truly can claim to be world-leading.

Finding a sustainable aviation fuel is likely to remain a long-term problem owing to energy content, usability and technical viability compared with jet fuel

In addition to SAFs, the RAF Rapid Capabilities Office is investigating the use of Synthetic Fuels made from CO2 and hydrogen using renewable energy in the manufacturing process; these fuels could save 80–90% of carbon emissions per flight. While these new approaches are environmentally friendly, they could also provide increased sovereign security, have maintenance benefits due to being chemically purer, and emit lower noise, heat and visual signatures. The RAF has had some success. Under Project MARTIN (working with Zero Petroleum), in a world-first, it flew the first microlight aircraft powered by synthetic UL91 gasoline alone. But we shouldn’t get too excited just yet; both SAF and synthetic fuels are in short supply. Global jet fuel consumption is currently 320 million metric tonnes per year, whereas the entire global SAF production is only 100,000 metric tonnes, and at a cost 10 times that of kerosene. Paul Stein, Chief Technical Officer at Rolls Royce, claims that ‘if SAF production can be scaled up – and aviation needs 500 million tonnes a year by 2050 – we can make a huge contribution for our planet’.


Some organisations are looking at the viability of electrification, popular with those who see the answer to climate change as ‘electrify everything’. While progress has been made with smaller, lighter aircraft, at present lithium-ion batteries do not offer the same energy density as other forms of propulsion. To its credit, in keeping with its ambitious ethos, the RAF is seeking to operate a fleet of emission-free, light training aircraft by 2027 under Project TELUM. Exploiting existing technology, this project would be an eye-catching achievement for RAF sustainability. Not only would an electrified training fleet provide a quick win on the decarbonisation journey, but it could also offer the RAF a position from which to transfer the concept into larger platforms if battery technology advances. However, aviation looks likely to continue to be difficult to electrify in the short term.

Limitations in electrification have led aviation communities to look more seriously at hydrogen. Grazia Vitaldini, Chief Technology Officer at Airbus, has described hydrogen as ‘one of the most promising technology vectors… fulfilling the basic human need for mobility in better harmony with our environment’. For this reason, Airbus has slowed its R&D in electrification, notably ending its E-Fan X project in April 2020, and placing hydrogen-fuelled propulsion systems at the heart of Project ZEROe - a multibillion-euro EU package for the generation of zero-emissions aircraft. However, while hydrogen has a higher energy by mass than jet fuel, it has a lower energy by volume, and the energy density of liquid hydrogen is about a quarter of that of jet fuel – storage tanks would need to be four times larger than present requirements. Equally, production of liquid hydrogen is four times as expensive as conventional jet fuel and, even though prices are expected to drop with increased efficiency, McKinsey claims it is likely to remain at least twice as expensive as fossil fuels for the next few decades. Armed with this information, 2040 appears overly ambitious for net-zero aviation, despite the greenest of intentions.

So What?

The fact remains that finding a sustainable aviation fuel is likely to remain a long-term problem owing to energy content, usability and technical viability compared with jet fuel. Though the plethora of alternatives to Jet-A will allow the RAF to spread-bet options, staggering its decarbonisation journey through SAF and synthetic in the short term, the reality remains that a significant technological breakthrough is required if eco-friendly propulsion is to become viable for aviation. There is a growing belief that technological measures alone are insufficient to limit annual carbon emissions. It is highly likely that the RAF will have to invest more into carbon sequestration and offsetting to achieve net zero and beyond that, carbon negative. The introduction of the global market-based Carbon Offsetting and Reduction Scheme for International Aviation in 2021 further reinforces this belief. Fortunately, the RAF is taking steps to green its estate.

Net-zero Estate

Given the difficulties outlined above, and the semi-dependency on civilian industries for R&D, the RAF estate offers the most potential for immediate change, accounting for 25% of CO2 emissions. With the ability to take a greater ownership of the issue, the RAF’s Astra programme has launched a 10-year plan to improve accommodation and facilities, while Project VITAL has a sustainability focus, establishing RAF Leeming as a ‘living laboratory’ to achieve a net-zero airbase by 2025.

The decision to target net zero by 2040 may seem overly ambitious, but has already been justified with pilot projects delivering significant financial savings and increased energy resilience

Work includes cutting-edge solar technology, carbon sequestration, insulation of infrastructure, and the investigation of geothermal, hydrogen and electric as potential energy sources for the base. A study of existing infrastructure intends to improve energy efficiency through retrofitting, while a ‘no regrets’ policy will implement readily available, simple, small-scale (and often cheaper) changes to achieve quick wins. It will also review how the runway maintenance programme could incorporate ground source heat pump technology, and whether lightweight solar panels can be fitted to aging hangar rooves.

This excellent work is being conducted in partnership with Newcastle University to create a ‘framework to enable the rapid impact assessment of a range of proposed changes in behaviour and emergent decarbonising technologies and innovations’. This relationship attempts to address the tendency for the military to rely on commercial off-the-shelf solutions, allowing for collective working with academia and industry from conception to completion. Furthermore, the RAF is underpinning this work by addressing human behaviours, including plans to spread the ‘reduce, reuse and recycle’ message, to minimise work travel and to reduce the use of single-use plastics. Progress is not solely limited to RAF Leeming; RAF Marham is the UK’s first military base to run almost completely on green electricity using biogas. This transition has increased the RAF’s energy resilience by reducing dependency on civilian infrastructure, often powered by overseas energy, while saving around £300,000 per year on energy expenditure. Once concepts have been proven within pilot sites, the RAF will roll out plans across its UK basing; future work will investigate how to transfer ideas into a deployed infrastructure. This deliberately scalable approach de-risks the transition to carbon-reduced operations at home and overseas.


The RAF has outlined lofty ambitions but faces a sky-high problem in achieving carbon-neutral aviation. The service is ably collaborating with the civil aviation industry, academia and other national air forces to find a common solution; perhaps a greater integration across the services would prove equally beneficial. Joint schemes to trial concepts in basic training platforms have provided a regular drumbeat of work while ensuring the RAF retains Defence headlines in this area. This success is reinforced through the passionate communication of CAS, underlining the importance of securing a senior champion to force through difficult changes. The decision to target net zero by 2040 may seem overly ambitious, but has already been justified with pilot projects delivering significant financial savings and increased energy resilience; equally, the date could be deliberately provocative, aimed at creating healthy competition among the services. What is certain is that while industry may claim that 2050 may not be possible for clean aviation fuel, there is increasing global pressure to accelerate environmental targets ahead of this date. In this regard, Defence, and not just the RAF, needs to work to the most ambitious of timeframes.

The views expressed in this Commentary are the authors’, and do not represent those of RUSI or any other institution.

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Lieutenant Colonel Alistair Beard

Former Army Visiting Fellow

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Dr Sarah Ashbridge

Affiliate Expert

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