A UK army division can consume roughly 800,000 litres of diesel per day during high-intensity warfare, equivalent to the energy output of a medium-sized nuclear reactor. Meeting that demand represents a growing operational challenge, with diesel now as much a logistical vulnerability as an energy source. Supply convoys rely on large numbers of trucks, ships and personnel, remain highly vulnerable to attack and consume massive quantities of fuel themselves.
“There are serious questions about whether global diesel supply can scale to meet future demand and how long it will remain a reliable source of energy,” John Hollingworth of Mahle Powertrain tells Professional Engineering. “That is creating real interest in both alternative fuels and more efficient use of existing platforms.”
Hydrogen is often positioned as a direct replacement fuel, but in defence the more immediate opportunity lies in adapting existing platforms rather than developing new vehicles outright, Hollingworth says. Military vehicle platforms are expensive and slow to develop, remain in service for decades and must meet stringent reliability requirements throughout their lifecycle. That reality is pushing attention towards retrofit solutions.
Mahle Powertrain, part of the global automotive technology developer Mahle Group, is working on approaches to integrate electrification and hybridisation into existing internal combustion vehicles. Such systems offer several tactical advantages, including reduced acoustic and thermal signatures during operations, making vehicles harder to detect.
Simulation plays a central role in development. Mission profiles are modelled virtually across terrain, load and operational tempo to understand how energy is consumed and how hybrid architectures behave under realistic conditions, before any physical hardware is developed.
“It’s unlikely that the MoD (Ministry of Defence), for example, will suddenly change the powertrain because it’s committed to the fleet it already has. That means our most realistic option is to develop retrofit solutions – but equally, having to work within pre-determined spaces is one of the biggest engineering constraints,” Hollingworth says.
Much of the underlying technology is already established and proven in automotive applications, including Mahle’s range extender concepts where combustion engines primarily generate electricity rather than directly powering wheels. For defence, the challenge is therefore less about invention than integration – albeit under strict operational constraints.
In April 2026, Mahle Powertrain successfully converted a 13-litre heavy-duty engine to run purely on hydrogen. The demonstration was part of Project Cavendish, an ongoing £9.8m programme supported by the Advanced Propulsion Centre UK to develop a hydrogen powertrain for heavy-goods transport, with clear defence applications.
Beyond vehicles, a second opportunity for hydrogen lies in stationary power generation. The power needs of military bases in conflict zones or supporting relief efforts are typically met by networks of diesel generators. These provide the one to five megawatts a day typically required for communications, information processing, climate control and other personnel needs.
One alternative concept is a containerised hydrogen power generation – a hydrogen-fuelled combustion engine housed in modular container units and deployed as mobile electricity sources. Power is generated at the point of use, reducing reliance on transported diesel fuel and further supporting a transition to hydrogen-powered vehicles.
Hollingworth envisions “hydrogen power plants in a box” powering both military bases and vehicles, with water as the sole byproduct, which could be captured and used for either cooling equipment or filtered for drinking. As with hybridised powertrains, much of the knowledge and systems have already been tested and proven in civilian applications, he says.
Storage remains the principal barrier, Hollingworth notes. Compressed hydrogen gas requires high-pressure containment and is highly volatile, while liquid hydrogen introduces cryogenic complexity and demands entirely new supply chain infrastructure. Both are difficult to reconcile with battlefield logistics. Hollingworth believes solid-state hydrogen will ultimately be the enabler, although it remains at an early stage of development.
For Mahle Powertrain, the opportunity lies in transferring its proven automotive technologies into defence applications. “Much of the engineering capability required to support hydrogen combustion, hybridisation and electric powertrains already exists,” Hollingworth says. “But defence procurement remains fragmented across multiple stakeholders – military organisations, prime contractors and multiple tiers of suppliers.
“Each operates on different timelines and priorities, with their own processes and systems. There is no single decision point. The system-level change required will only occur when, and if, the MoD, OEMs, tier-one suppliers and defence industry bodies all come together at the same time to drive it.”
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.