THE MARINES OF INDIA COMPANY harbored grave doubts about the experimental solar-power gear they were ordered to tote from their beachside base at Camp Pendleton to the grimmest, toughest war zone of Afghanistan. They arrived far more interested in armor to protect them while they patrolled the "Fish Tank," a booby trap-laden settlement next to their base, than in thin-film photovoltaics that might protect the planet from their carbon bootprint. India Company had encountered up to 15 roadside bombs a day, and individual platoon casualty rates had run as high as 25 percent killed or wounded. Tree hugging didn't seem like much of a survival skill in a place where a single false step could cost your legs—or worse.

"I was a skeptic," Gunnery Sergeant Willy Carrion says, in comments passed on from Afghanistan by military officials. "As Marines, we do not always like change. I expected [the solar gear] to be a burden."

An India Company soldier connects a radio battery to a portable, solar recharging system—part of the Army's ExFOB gear—at Patrol Base Gumbatty, in Afghanistan's Sangin District. | U.S. Marine Corps/Gunnery Sgt. William Price

But then they put it to the test. The portable solar generators and battery packs that powered the Marines' lights, radios, and computers day and night ran quietly, coolly, and cleanly, unlike the loud, cranky, jet-fuel-sucking generators they normally used. Camp Jackson, India Company's forward operating base, went from a noisy, easy target for insurgents roaming the night to a silent, stealthy, safer outpost. The 20 to 25 gallons of fuel it previously took to power a platoon each day suddenly lasted more than a week—which meant fewer fuel convoys, with their notoriously high casualty rates; fewer collisions with roadside improvised explosive devices (IEDs), and fewer Marines assigned to convoy duty instead of their primary mission.

Portable solar chargers allowed Marine patrols to spend weeks away from their Camp Jackson stronghold in the Taliban-infested Sangin district of Helmand Province without needing to lug extra batteries for their radios and other devices. This is no small matter: A modern infantry soldier may have to carry five pounds of batteries a day in the field. The heavy load displaces ammunition and demands regular replenishment missions that are as dangerous as fuel convoys. Fold-up solar chargers eliminated all that, according to First Lieutenant Josef Patterson, an India Company platoon commander. One set of batteries for each device lasted three weeks. "If I do not have a radio, I'm lost," Patterson explains. "So that was huge. I'm completely sold."

India Company is now the greenest fighting unit in the U.S. military. Its battle-tested package of solar gadgets—collectively dubbed the ExFOB (Experimental Forward Operating Base) by the acronym-loving military—has been a hit with the troops on the ground. Most of the fuel consumed in a combat zone powers electric generators, not vehicles, which makes solar a perfect alternative. The best evidence of this: Other units are clamoring for the same gear. India Company has become the model for a leaner, meaner, lower-carbon fighting force.

The USS Makin Island, an amphibious assault ship, can go from muscle car to hybrid with the flip of a switch. | U.S. Navy/Petty Officer Third Class Peter Merrill/Released

The Department of Defense uses more petroleum (and energy) than any other organization on the planet—$13 billion to $18 billion worth a year, depending on who does the math. That accounts for more than 80 percent of the federal government's energy tab. But after years of resistance, Gunnery Sergeant Carrion's suggestion is now Pentagon policy. The U.S. military, despite being stretched thin by eight years and a trillion-plus dollars spent in Iraq, Afghanistan, and now Libya, is taking on another controversial, long-term mission: to defend America without depending on oil.

The pride of the Navy is no longer the iconic Nimitz-class nuclear-powered floating airfield or the deadly Aegis missile destroyer with gas-turbine engines that suck 34 gallons of fuel a minute. Now it's the nimble, multipurpose amphibious assault ship USS Makin Island, an electric hybrid that can carry an entire Marine expeditionary unit, complete with tanks and aircraft, while using 60 percent less fossil fuel than its predecessors. Meanwhile, spurred on by glowing reports from India Company, the Marine Corps is equipping other units with the ExFOB and testing a new round of green battle gear at its desert training facility in Twentynine Palms, California, including a renewable-energy water-purification system intended to reduce the dangerous trucking of bottled water.

The Army is pursuing an aggressive "net zero" goal for its permanent bases worldwide, balancing production and consumption of energy, water, and waste so that they total out to zero. Plans have been approved for dozens of solar-power installations at bases around the world, and testing is ongoing for combat technologies such as an electric hybrid dune buggy for special forces, mobile factories that turn battle-zone waste into renewable fuel, and portable hybrid generators and smart "microgrids" that provide instant green power for far-flung outposts.

The Air Force, the military's biggest oil hog, is certifying fighters, bombers, and cargo jets to run on a mix that's 50 percent lower-carbon renewable biofuels. Once-cutting-edge stealth engineering is now old hat; the sexy new topic in aviation tech is fuel-producing algae. Tanks and jeeps—not to mention military garbage trucks and the 164,000 other noncombat vehicles that service military bases—are next in line for biofuels and hybridization.

Military officials are quick to make clear that this effort has nothing to do with political correctness, saving endangered species, or even slowing the global warming caused by the military's 300,000-barrels-a-day oil habit. "It's about cost. It's about national security. And it's about the burden in blood," says Bill Browning, a member of the Defense Science Board's energy task force (now disbanded) and a founder of the environmental consulting group Terrapin Bright Green. He points to a simple, terrible statistic concerning Iraq and Afghanistan: "Half the casualties in these conflicts have been fuel-convoy related."

MV-22 Osprey's tilt rotors enable it to land on compact ships. | U.S. Navy/Chief Petty Officer John Lill/Released

In 2007, one out of every 24 fuel convoys in Afghanistan, and one out of 38 in Iraq, led to a military fatality, according to an Army study examining the link between casualties and energy. The 6,000 fuel convoys that year imposed such a huge cost in lives, manpower, and money that the Pentagon could no longer ignore it, Browning says. "We call them convoys, but we might as well call them targets," says James Valdes, an Army scientific adviser and designer of a prototype trash-to-energy system for combat zones. Adds Paul Skalny, director of the Army's National Automotive Center in Detroit, "This is the number that matters: For every 1 percent of fuel we don't have to burn, 6,444 fewer soldiers have to be involved in convoy operations. And those are sons and daughters and husbands and wives who get to go home to their families someday."

In addition to mortality statistics are some grim budgetary realities. Getting fuel to combat troops in Afghanistan costs between $25 and $50 a gallon, and sometimes as much as $400. Even at the most peaceful outpost, it's never lower than $14 a gallon. Says Tom Hicks, the Navy's first deputy assistant secretary for energy (a post that didn't exist until last year): "We've realized that the best barrel of oil is the one we don't use."

Hicks's boss, Navy secretary Ray Mabus, is among the most vocal of the military's energy hawks. The former Mississippi governor publicly decries oil dependence for making our country and military "far too vulnerable." Mabus promises a "great green fleet" powered by renewable energy, starting with a carrier strike group to be demonstrated next year, and a Navy-wide conversion to 50 percent oil-free energy on land, at sea, and in the air by 2020, with a mix of solar, wind, geothermal, biofuel, and nuclear power. This is a tall order, given that between the Navy and the Marines under his command, Mabus's empire includes 290 ships; 3,700 jets, planes, and helicopters; 50,000 vehicles; and more than 72,500 buildings.

The clandestine extended-range vehicle (CERV), a diesel-electric combat vehicle, can switch to silent running. | Courtesy of Quantum Technologies/Vachelle Poetoehena

How can Mabus get away with such a commitment in a bad economy and with a fractured Congress threatening to pull the plug on environmental and energy initiatives? Simple: Just as President Barack Obama pushed renewables while avoiding the word "climate" in this year's State of the Union address, Mabus and other defense leaders downplay any connection between a sustainably powered military and fighting climate change. Sharon Burke, the new director of defense operational energy plans and programs—the closest thing to an energy czar that the Pentagon has ever had—used this strategy when confronted during her confirmation hearings last fall by climate-change doubter-in-chief Senator James Inhofe. Burke shrugged off his suggestion that she was making carbon reduction her priority, saying that her charge was to "improve the military's energy security" and make sure that the Pentagon factors in the true cost of energy for its equipment, purchases, and operations. But she acknowledged, "They are linked together. . . . If we do it right, that will be one of the results, cutting greenhouse-gas emissions. But that's not the role of this job."

It turned out that talking about how a terrorist strike far smaller than 9/11 could cripple America's power grid (and most of our military bases along with it), and detailing the budget-busting specter of $400-a-gallon fuel for military Humvees that get as little as four miles per gallon, provided framing that even the most die-hard congressional climate skeptic could not easily dismiss. Green power, the energy hawks insist, makes the military stronger. No less an authority than Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, says, "Energy security needs to be one of the first things we think about, before we deploy another soldier, before we build another ship or plane, and before we buy or fill another rucksack."

The traditional attitude about energy at the Defense Department, Mullen admits, has been "Burn it if you got it." So its embrace of sustainability represents "a severe challenge," says Christine Parthemore, a fellow at the Center for New American Security. But, Parthemore points out, this is no more daunting than the Navy's evolution from sail to coal to oil to nuclear. Along the way, she says, the military helped lead worldwide energy changes by seeding and building markets for new technology—something the Pentagon appears to be trying to do once more, this time for solar, biofuel, and other alternative energy sources. "DOD is a huge energy consumer," Parthemore says. "Doing this gets the private sector up and running and innovating."

ALTHOUGH THE GREEN PUSH IS COMING FROM THE MILITARY LEADERSHIP and the White House now, not all of the military's planet-friendly projects have been the result of top-down policy changes. Some have come from within the ranks—a base commander scrounging funds for a solar-power installation or seeking Leadership in Energy and Environmental Design (LEED) certification for a new building. Even the lauded hybrid ship Makin Island came as an afterthought. The seven earlier ships in its Wasp class of amphibious assault vessels all burned petroleum to generate steam, a reliable but inefficient technology gradually being phased out. Ship designers realized that maybe this eighth and last ship could take advantage of its electrical-generating capacity if they added a bank of electric motors. Suddenly, the Navy had a very big floating Prius on its hands.

Instead of old-school steam boilers, the Makin Island has two 35,000-horsepower gas turbines that provide instant acceleration and speeds of up to a brisk 25 knots. But they're still gas guzzlers at low speeds, which is where a bank of 4,000-kilowatt diesel-electric generators and twin 5,000-horsepower electric motors comes in. With the flip of a switch, "we go from muscle car to hybrid," Chief Aaron Suarez says as he monitors the computerized graphical displays in the control center at the heart of the ship. "Me, I like muscle cars, so I like the gas turbines. But you can't beat the mileage of the hybrid."

"The bottom line is, I can stay in the fight longer," says Captain James W. Landers, the Makin Island's commander. "Using a third of the fuel gives us enormous flexibility." He points to several thick black rubber hoses running along the side of the ship and into the hull, tapping into its 2-million-gallon fuel supply. "Those are there because I can share when my sister ships run low on fuel." Designed to carry 800 Marines in addition to its crew of up to 1,000, the 847-foot Makin Island is a rapid-response warship that resembles a small aircraft carrier. Its landing deck, with its vertical takeoff and landing capability, accommodates helicopters, the tilt-rotor MV-22 Osprey, and the AV-8B Harrier jet.

The Makin Island runs all-electric at speeds of up to 12 knots—which it maintains during 70 percent of its time at sea. According to Mabus, it saved $2 million in fuel costs on its maiden voyage alone, from its shipyard in Mississippi to its homeport in San Diego. The Navy estimates that the $2.5 billion ship should save more than $250 million in fuel costs over its lifetime. The ship also features an advanced reverse-osmosis desalination plant that uses no toxic chemicals, emits only salt, and has enough capacity to supply its needs and simultaneously bring freshwater to disaster areas. Its excess electrical-generating capacity could also provide stricken communities with power for medical and rescue operations. Still, Landers points out, the Makin Island is not a green ship, only a step in the right direction: "We're still burning dead dinosaurs and making black smoke. Just a lot less of it."

The next version of amphibious assault ships, the America class, which will debut next year, will incorporate the same hybrid engines, and the Navy is planning to install the electric-drive system in new destroyers as well. Ten new ships will be coming on line every year for the next five years, giving the Navy a chance to gradually green the fleet and retire some of its worst oil hogs. Mabus has talked about retrofitting some existing ships to become hybrids too, but for the most part, the Navy is stuck with the ships it has now for the next 20 to 40 years.

That's why the military considers biofuels such an important near-term strategy for green progress. The Air Force and the Navy are taking the lead in developing biofuels for aircraft (vehicles, ships, and generators are next in line) from nonfood crops such as the camelina seed and algae. Further out on the horizon may be jet fuel from the emerging "electrofuels" industry, which uses microbes and electrosynthesis, photosynthesis's more powerful cousin. The Advanced Research Projects Agency-Energy and the Energy Department are throwing billions of research dollars at electrofuels, which they consider one of the more promising paths to fossil fuel independence to develop in many years.

In March, the Air Force Alternative Fuels Certification Division demonstrated that biofuel performs just as well as fossil fuels in the F-22 Raptor fighter jet. Commercial airlines are even more eager to see the industry ramp up, says Jeff Braun, the division's chief, with several firm commitments to buy biofuel as soon as it is available in commercial quantities. For the military, Braun notes, biofuels represent an energy "holy grail": domestically controlled fuel that can be produced anywhere the military needs it.

Not everyone is convinced. The Rand Corporation recently criticized the military's plans for biofuel, predicting that it would remain a niche industry incapable of providing the volume that the military needs at a price that could compete with oil. The Navy's Hicks counters that military purchases of biofuel, as they move from tens of thousands of gallons to tens of millions, will drive innovation and bring down costs. He cites as precedent such military-turned-commercial products as night-vision goggles, GPS devices, and even the Internet, all of which started out as expensive niche defense technologies. In fact, says Hicks, a former EPA and U.S. Green Building Council official who helped develop both the Energy Star program for buildings and the LEED rating system, "from what we can see already, we expect cost parity with petroleum by 2016."

MANY OBSTACLES STAND IN THE WAY of the military's big green goals, starting with the fact that most military housing and many other Defense Department buildings lack electrical meters—making it difficult to weed out inefficiencies. The armed services have recently been on a crash course to install "smart meters" but are still barely halfway there. An even greater energy and security concern is that almost all military bases—even those with solar or geothermal power plants attached—are dependent on the commercial grid for power. In the World War II era, most bases generated their own power, but that capacity gave way to privatization, leaving most bases vulnerable to grid sabotage while also complicating plans to green military electricity.

Then there's the flagship 500-megawatt solar project announced with great fanfare two years ago for Fort Irwin, in the California desert. There's been little progress since the announcement because the military belatedly realized that the infrastructure doesn't exist to transmit that much renewable electricity from the base to the grid. An ambitious vehicle project called the clandestine extended-range vehicle (CERV) actually got built in prototype, but might stay there. It's a diesel-electric hybrid that offers a silent all-electric mode highly sought after by Special Forces units. The CERV was intended to become the model for a whole range of more-fuel-efficient combat vehicles, but funds dried up, and a decision on whether to move beyond the four prototypes was delayed until next year.

An uncertain fate also awaits the Army's promising tactical garbage to energy refinery (TGER) system, a mobile garbage disposal and power generator that can eat 2,000 of the 2,500 pounds of waste that a 550-soldier brigade produces each day in the field—from food scraps to ammo wrappers to plastic bottles. Depending on its type, the refuse is turned into either a synthetic gas similar to propane or liquid ethanol, both of which are then combined into an aerosol that powers an electric generator. After successful field tests in Iraq in 2008, the project has stalled for lack of funding. An even more fundamental hurdle facing the military's green mission is that despite the ambitious goals set by each branch, there is still no overarching strategy from the Pentagon. The new defense energy leader, Burke, is charged with crafting one; she just returned from a long trip to Afghanistan and Iraq to research that strategy, which was due in May. Meanwhile, her old colleague Parthemore has coauthored a report recommending a straightforward, radical goal that would revolutionize the military and the industries that serve it: "To ready America's armed forces for tomorrow's challenges, DOD should ensure that it can operate all of its systems on non-petroleum fuels by 2040."

The Marines of India Company in Helmand Province have less lofty but more immediate goals: more solar generators and battery chargers, and fast, says Major Sean Sadlier, the Marine's energy liaison officer. "Every bit of relief matters to heavily engaged units and enables them to be more combat effective." Marines aren't out to save the planet—just to win the fight.