It looks like the US Army is trialling several fuel-efficient technologies in two models of humvee codenamed "FED Alpha" and "FED Bravo". "FED" is short for "Fuel Efficient Ground Vehicle Demonstrator". While it's not clear whether these prototypes will share their improvements with other military vehicles, if they prove successful, it's not a huge leap to think they'll make their way into other mobile war machines.
According to engineer Steve Framer of the US Army Tank and Automotive Research, Development and Engineering Command (or TARDEC, for those of us who enjoy breathing), the new humvees have more armour than current service models, but consume as much as 70 per cent less petrol while in operation (the average humvee gets 100km per 20L, so it's quite a saving). A redesigned 150kW, four-cylinder diesel engine and six-speed drive train are complemented by a rear solar panel. Low-rolling resistance tires apparently cut fuel usage by seven per cent by themselves.
So, no tanks just yet, but you can imagine they're just around the corner. In fact, they gave it a go back in 2007. There's just something less... manly about plugging a 60t armoured machine that can shoot explosions into a power socket and chilling while it charges.