The US Navy will formally deploy its so-called "Great Green Fleet" on Wednesday (local time), sending warships to sea on biofuels.
It comes even as oil prices have dropped 70 percent since congressional Republicans first criticised the high cost of alternative fuels.
Navy Secretary Ray Mabus told Reuters the deployment is the next step in a fleet-wide effort that has seen the Navy cut its oil consumption by 15 percent since he took charge in 2009 and the Marine Corps curb its use by 60 percent.
A focus on energy and energy-saving technology gives the US Navy a military advantage, Mabus said. An amphibious assault ship like the USS Makin Island, which uses a dual electric-diesel propulsion system, can stay on station three times longer than a conventionally powered vessel, he said.
"It gives us an edge tactically, it gives us an edge strategically," Mabus said. "It keeps fuel from being used as a weapon against us."
Mabus and US Agriculture Secretary Tom Vilsack will be on hand in San Diego on Wednesday for the formal deployment of the Great Green Fleet, when diesel ships in a carrier strike group led by the nuclear-powered USS John C Stennis refuel with a diesel-biofuel blend.
Mark Cancian, an analyst at the Center for Strategic and International Studies and former White House budget official, said the initiative is as much about environmental symbolism as cost savings or tactical advantage.
Many congressional Republicans objected three years ago when the Navy sought and won support for defence subsidies to help three private firms build biofuel refineries. With oil now selling around US$30 a barrel (NZ$47.03), that scepticism remains.
"They have not changed their position, which is that these are too expensive and not needed," Cancian said.
The defence department uses about 53 million litres of fuel a day, with the Navy responsible for about a quarter of that, according to figures from the Defense Logistics Agency.
When the Navy first tested biofuel versions of marine diesel and jet fuel in 2012, it spent eye-popping sums for small amounts, four times the price of conventional fuel.
The fuel being used for the Great Green Fleet deployment is a competitively priced blend of 90 per cent diesel and 10 percent biofuel based on a beef tallow feedstock, Navy officials said.
To boost production of alternative fuels, the Navy has awarded US$210 million to help three firms build refineries to make biofuels using woody biomass, municipal waste and used cooking grease and oil. The US Department of Agriculture is providing an additional $161 million in crop supports.