As defence looks to reduce its carbon emissions, the British Army vehicle fleet is being put forward for potential hybrid transformation.
The Jackal, the Foxhound and the MAN supply truck are all part of the experiment at Millbrook Proving Ground in Bedfordshire.
A major climate change report this year detailed the military's plans to help the UK reach net-zero emissions while maintaining capability.
Lieutenant Colonel Ed Sutthery, head of British Army Innovation, Research and Experimentation, explained some of the potential benefits if defence turns to the hybrid solutions.
Silent vehicle running to give "greater power demand" could eliminate the need for personnel to turn on the engine in an overwatch position, he said, reducing the risk of compromise.
Once vehicles enter electric mode the only audible noise "is the noise of the wheels on the Tarmac," he added.
The pictures below offer a glimpse of the testing in Bedfordshire:
Currently, defence accounts for half of all the Government's carbon emissions and wants to hit net-zero by 2050.
With this in mind, it has turned to Sheffield-based electric and vehicle manufacturer MAGTEC to strip apart the vehicles for transformation – part of £7m of defence-funded research into hybrid vehicles.
In the reconfigured Jackal, an electric generator takes the place of the standard gearbox while an electric motor is designated to each of the four wheels.
With the left and right-hand side wheels capable of moving in opposite directions, the hybrid Jackal can pivot and turn on the spot.
This is "something that only tracked vehicles up to now have been able to do," said Marcus Jenkins, managing director of MAGTEC.
In addition, the hybrid vehicles can supply power to external sources.
Watch: How could the military adapt to climate change?
With its engine running, the MAN support vehicle can produce 500 kilowatts of electricity – equivalent to nine generators.
Using only its batteries, the redesigned workhorse of the service has enough energy to keep the average UK home fully powered for 18 days.
Bedfordshire's experiments will continue until Christmas before the Army itself puts the hybrid concept models to task in field testing.