Sapinos Jamod ajcpsnevaui.

The Defense Department is the largest single user of energy in the United States, if not the entire world. That dependence costs the military billions of dollars in fuel a year and requires troops to undergo dangerous delivery missions.

In a future war, the Defense Department will need renewable energy sources that can juice up soldier equipment, sustain weapon systems and power bases, all while reducing the department's logistical tail and reliance on fossil fuels, experts said.

"Napoleon said that an army runs on its stomach. Well, the truth is the army of today runs on oil," said Andrew Holland, senior fellow for energy and climate at the American Security Project, a Washington, D.C.-based think tank.

During fiscal year 2012--the most recent data available--the Defense Department spent $16.4 billion on 104 million barrels of liquid fuels for various operational energy uses, according to the office of the assistant secretary of defense for operational energy plans and programs.

The military derives its power almost exclusively from petroleum, Holland said. That dependence tethers the armed services to expensive oil and forces them to transport large quantities of fuel in dangerous and sometimes contested areas, he said.

Nuclear fusion reactors may offer troops plentiful energy on demand in a safer and less expensive way, he said.

The reactors work by taking hydrogen and heating it to high temperatures, Holland said. The hydrogen then fuses into helium and emits a large amount of energy that can be converted into electricity.

Unlike nuclear fission reactors, fusion reactors are much safer, he noted.

"There is no chance of a meltdown and there is no radioactive material left behind," he said. A fusion reactor could be useful on an isolated base somewhere in the Asia-Pacific region, he added.

"A Navy/Marine base in Guam is powered all by diesel fuel that has to be shipped in at great cost. ... If you could run that base on a fusion generator that requires no fuel, you could save a lot of money and cut your logistical tail significantly," he said.

The ability to produce energy on demand while reducing logistical operations could be critical during a potential conflict in the area, he said.

"In certain future wars, especially in the Asia--Pacific, we have potential adversaries that ... can certainly [threaten] the more vulnerable tail of the fleet and then force the fleet farther away," Holland said.

Fusion reactors could be operational within...