What does the U.S. Army’s planned acquisition of 4,000 golf-cart-looking electric vehicles have to do with America’s clean-energy future?

A lot, potentially. It’s the latest sign that the Pentagon, reeling from high fuel costs and an even higher cost in human life from long and vulnerable fuel-supply lines, is finally starting to take energy efficiency seriously, seven years after first flagging the issue. And when the Pentagon throws its weight and considerable budget behind something, from aviation to the Internet, the innovations inevitably tend to trickle down to the rest of the national fabric.

Humble beginnings, big promise (US Army)

For now, the Army’s transformation involves baby steps—a few bases using more solar power, some turning to geothermal. The electric-car order is designed to replace non-combat vehicles on select military bases, and will save 11.5 million gallons of fuel. Eventually, the Army could order up to 28,000 electric cars for use on bases.

But the real fuel-efficiency action could be found in the Army’s combat fleet, including the heavy vehicles in mechanized and armored divisions. There’s no shortage of reasons. The Pentagon pays a lot more for fuel than list prices; peacetime fuel costs for all services total $13 a gallon. In war zones that require long supply convoys or air-lifted fuel, that can skyrocket to as much as $400 a gallon, the Pentagon says. Multiply that by the 600,000 gallons an armored division uses every day (the Abrams tank gets half a mile to the gallon), and the economics alone are overwhelming.

But for the Defense Department, operational reasons still trump economics. Greater fuel efficiency by combat vehicles will give commanders more flexibility. Most importantly, as the Iraq war has shown, severing the “fuel tether” can save lives. About 70% of supply convoys carry fuel, often just diesel for generators. Convoys are the main target of deadly insurgent attacks.

That’s the main reason that Marine Maj. Gen. Richard Zilmer, based in the conflictive Anbar province in western Iraq, sent his bosses a “priority one” request for more renewable energy in the summer of 2006 (which was promptly denied). More solar panels at forward bases would have meant fewer vulnerable supply convoys.

The idea was enshrined in a now-famous 2001 Pentagon study that recommended making fuel efficiency a cornerstone of the future army. Its recommendations—including making fuel-efficiency a pre-condition for Pentagon vehicle procurement–weren’t acted on. Earlier this year, the Pentagon revisited the subject in the “More Fight-Less Fuel” report with the explicit goal of adding more “teeth” to combat forces while trimming their logistical “tail.”

The most likely beneficiary? Engineers are working on future combat systems, like a hybrid-electric tank engine, but that could be a decade away. Closer to fruition is the replacement for the 25-year old, much-maligned Humvee tactical vehicle. A spate of defense contractors are currently building the new Joint Light Tactical Vehicle, which should be in production by 2012. In addition to all the other obvious improvements, like armor protection, the JLTV will include a hybrid version to make sure fuel-efficiency makes the transition from Pentagon memos to the front lines.