When government ignores market signals to mandate the use of costly “green” energy sources, it’s clear that resources are diverted from their best use. While wasteful, the process is not necessarily dangerous.

But Jim McTague devotes his latest “D.C. Current” column in Barron’s to a case in which efforts to “go green” could have a clear negative impact on the one area in which government clearly plays an important role: national defense.

Shoot — but don’t pollute! The Navy next month will sail into the Pacific with a battle group of ships and carrier-based aircraft powered by both nuclear energy and a 50/50 blend of biofuel and petroleum products, in a quixotic demonstration that our warships need not be tethered to oil from hostile nations and that they are doing their bit to battle global warming. The so-called Great Green Fleet, the brain child of Navy Secretary Ray Mabus, will participate in the bi-annual Rim of the Pacific Exercise off Hawaii, along with allied ships from South America, Asia, and Australia running on conventional petroleum fuels.

In addition to making a green statement, this exotic exercise could become an issue in this year’s presidential election campaign. Critics paint the exercise as a costly extravagance in an era of shrinking defense budgets. Cuts have weakened the fleet at a time that the China is expanding its navy and using it to menace Japan and the Philippines. The U.S. Navy, whose budget is down 1.5% from fiscal 2011, is economizing by cutting back on new ships and retiring seven cruisers earlier than anticipated, according to the Navy Times. …

… Republicans in Congress — prompted by complaints from front-line Navy and Marine officers — have described Mabus’s moves as an Obama energy boondoggle. Not only is the cost of biofuel high but U.S. dependence on OPEC oil is fast fading because of advances in drilling technology and new oil and gas discoveries. An angry Republican Sen. John McCain at a March Senate Armed Services Committee hearing compared the Navy’s biofuel program to Solyndra, the politically connected solar-panel company that went belly-up despite $535 million in guaranteed loans from Obama’s Department of Energy.

Virginia Republican Rep. Randy Forbes has told Mabus that the Navy can ill afford to spend heavily on a biofuel experiment when the Navy can’t afford to keep enough fighting ships on the water. The cruisers retired because of funding cuts have the equivalent firepower of the entire Royal Navy, said Forbes, who is chairman of the Armed Services Subcommittee on Readiness.