They are set to be the future of stealth transport for soldiers - and can run on electricity and everything from petrol to olive oil.

The Defense Advanced Research Projects Agency, or DARPA, has shown off the two projects is had backed to create next generation stealth motorbikes.

The SilentHawk by Logos and the Nightmare from LSA Autonomy are both being funded by the agency.

The Nightmare Stealth bike from LSA Autonomy. The hybrid engine bike would use diesel, gasoline or jet fuel for normal operations. But when it gets closer to the enemy, it would run almost silently on electricity.

The two prototypes have been shown at the National Defense Industrial Association's Special Operations Forces Industry Conference in Tampa.

Both bikes feature cutting-edge hybrid multi-fuel engines that can burn a variety of combustibles from jet fuel to olive oil.

'If it's gasoline, tell it it's gasoline, tell it it's something else. It will figure it out,' Alex Dzwill, and engineer with Logos, told Defence One.

When asked if you can run it on other fuels, such as olive oil, he said ' “Theoretically, yeah,” said Dzwill.

The bikes have two modes, a traditional 'loud mode', and a quiet mode that switches the bike to operating from a battery.

The loud mode is akin to a garbage disposal at around 80 decibels, while quiet mode is 55 decibels, about as loud as an indoor conversation.

The SilentHawk prototypes shown at the National Defense Industrial Association's Special Operations Forces Industry Conference in Tampa.

The idea is that for normal operations, the bike would use diesel, gasoline or jet fuel. But when it gets closer to the enemy, it would run almost silently on electricity.

According to its makers, Virginia-based Logos Technologies, the bike's louder mode would be slightly louder than the average vacuum cleaner, reaching up to 75 decibels.

The company also says it Silent Hawk could travel over difficult terrain on its hybrid engine over a sustained period at 55 miles per hour (88km/h).

The combustion engine will also be removable, which means Silent Hawk can become all-electric, and also shed weight or take out problem parts.

On its own, the bike's battery can power it for up to 50 miles (80km). However, the concept is still under development and further specifications have yet to be announced.

The SilentHawk bike can be customised for different operations, with carriers and camouflage.

SilentHawk is based on Alta Motors' electric racing bike, the RedShift MX (pictured). It uses Alta's chassis, while the hybrid engine is being developed by Logos

SILENT ELECTRIC AIRCRAFT COULD BE ROLLED OUT IN 20 YEARS The prototype two-seater electric aircraft by Airbus made its maiden flight in March last year Spectators at air shows are usually impressed by the boom of fighter jets flying overhead. But aeroplane fans at the Berlin Air Show were also wowed by the eerily quiet flight of Airbus Group's fully-electric aircraft last year. The prototype two-seater made its maiden flight in March but only took to the skies in front of the public in May. It was designed from scratch, from its electrical propulsion and energy management system to its safety features. Airbus hopes that the prototype is one step towards the aerospace industry using regional jets powered by hybrid electric engines, which would slash its carbon dioxide emissions. The development of a regional plane, seating between 70 and 90 people that can take off and land using electric power, could take between 15 and 20 years, Airbus Group Chief Technology Officer Jean Botti told reporters in Munich. Advertisement

The Defense Advanced Research Projects Agency (Darpa) began the motorcycle project last year, and has now granted its makers an award to develop it further.

Logos says it now plan 'to proceed with an aggressive Phase II program plan, with the goal of developing and testing the first operational prototype in only 18 months.'

Silent Hawk is based on Alta Motors' electric racing bike, the RedShift MX. It uses Alta's chassis, while the hybrid engine is being developed by Logos.

The U.S. Special Operations Command previously tried to use an all-electric Zero MMX bike for the same purpose, but the battery only lasted two hours.

It's not just commandos will soon be receiving steal motorbikes. In August, it was announced that police forces could use the bikes to approach criminals undetected.

The bike, designed by Zero Motorcycles in northern California, has a top speed of up to 98 mph (158 km/h), allowing police to chase criminals down if the stealth approach fails.