The sight of US army Humvee troop carriers stranded in the Iraqi desert waiting for refuelling tankers to catch up with them has not only alarmed commanders in the battlefield. It has also highlighted efforts by the US military to develop a new generation of vehicles that rely on new forms of propulsion, cutting the cost of fuel and reducing US dependence on foreign sources of oil for future global military missions.

The fuel cost numbers are startling. A gallon of modified jet fuel, which is used in tanks as well as aircraft, costs only 84 cents when bought wholesale from multinational oil companies such as Shell and ExxonMobil.