The United States and other countries represented at Rim of the Pacific naval war games underway in Hawaii’s waters are tapping alternative fuels and pursuing energy conservation measures, a top Navy official said.

Retired Vice Adm. Dennis V. McGinn, now serving as assistant secretary of the Navy in charge of energy, installations and environment, told reporters at a Ford Island news conference last week that through a initiative dubbed the “Great Green Fleet,” U.S. warships are burning a combination of 90 percent diesel and 10 percent biofuel from animal fat, which the Navy maintains is cost-competitive with traditional fuels.

Undersecretary of the Navy Janine Davidson, who joined McGinn at the news conference, said, “All this means is that we can go farther … stay out longer and deliver more firepower. So, it is all about combat-effectiveness.”

McGinn said eight countries participating in the maritime RIMPAC war games are using biofuels.

According to a Navy fact sheet, Secretary of the Navy Ray Mabus in 2009 issued five energy goals aimed at transforming the Navy’s energy use. One goal was to deploy the Great Green Fleet in 2016.

The term is a play on the Great White Fleet of Navy ships that circumnavigated the globe under President Theodore Roosevelt.

The centerpiece of the Great Green Fleet is the nuclear aircraft carrier USS John C. Stennis with Carrier Air Wing 9 and Destroyer Squadron 21 with guided-missile destroyers Chung-Hoon, Stockdale, William P. Lawrence and guided-missile cruiser Mobile Bay. The Chung-Hoon is based at Pearl Harbor.

The Navy said the cruisers and destroyers of the Stennis strike group all have stern flaps that modify the flow of water under the ship’s hull to reduce drag and resistance. Also, the USS Mobile Bay has a hull coating that makes it harder for barnacles and other organisms to attach to the ship. Both energy conservation measures reduce resistance through the water, thereby increasing fuel efficiency.

Embracing alternative fuels, energy conservation measures and operational procedures is helping the Navy to become a more flexible fighting force, McGinn said.

Also, McGinn said a federal appeals court ruling that struck down the Navy’s use of low-frequency sonar for training will not affect RIMPAC exercises, which involve 45 ships and five submarines from 26 nations.

On July 15 a federal appeals court ruled that the Navy was wrongly allowed to use sonar, which could harm whales and other marine life.

The 9th U.S. Circuit Court of Appeals reversed a lower-court decision upholding approval granted in 2012 for the Navy to use low-frequency sonar for training, testing and routine operations.

The five-year approval covered peacetime operations in the Pacific, Atlantic and Indian oceans, and the Mediterranean Sea.

McGinn said the Navy and the National Oceanic and Atmospheric Administration will together address the questions raised by the appeals court.

“We are tremendously responsible stewards of the marine environment, of all the environment,” said McGinn, who commanded the U.S. 3rd Fleet in 2000 and was the U.S. officer in charge of the overall coordination of RIMPAC that year. “We take seriously not just the need to provide national security, but to really treasure that which we are defending, and that is the fantastic natural environment, especially in a place like Hawaii and indeed the whole Pacific.”

Environmental groups led by the Natural Resources Defense Council filed a lawsuit in San Francisco in 2012, arguing that the approval violated the Marine Mammal Protection Act.

“We have every reason to believe that the Navy has been deliberate and thoughtful in its plans to follow NMFS guidelines and limit unnecessary harassment and harm to marine mammals,” the appellate ruling said.

However, the panel concluded that the fisheries service “did not give adequate protection to areas of the world’s oceans flagged by its own experts as biologically important,” according to a summary accompanying the court’s decision. “The result is that a meaningful proportion of the world’s marine mammal habitat is under-protected.”

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The Associated Press contributed to this report.